With this mod you can add two new payment plans, 1 featured we will call Featured+ and one regular, we call Regular+. You can adapt this tutorial to add as many payment plans as you would like to.

1. In this step you should add two rows in the PLD_CONFIG. You can use one of the following two methods.

Method 1: run the following Mysql query in phpMyadmin:

INSERT INTO `PLD_CONFIG` (`ID`, `VALUE`) VALUES
 ('PAY_NORMAL_ADV', '20'), ('PAY_FEATURED_ADV', '50');

Here 20 and 50 are the prices of the different plans, either change them before running the query or can just edit them in the admin panel when you are done adding the MOD.

Method 2:
in include/tables.php
FIND:

array ('ID' => 'PAY_NORMAL', 'VALUE' => '0'),
array ('ID' => 'PAY_FEATURED', 'VALUE' => '0'),
array ('ID' => 'PAY_RECPR', 'VALUE' => '0'),

REPLACE BY:

array ('ID' => 'PAY_NORMAL', 'VALUE' => '0'),
array ('ID' => 'PAY_FEATURED', 'VALUE' => '0'),
array ('ID' => 'PAY_NORMAL_ADV', 'VALUE' => '0'),
array ('ID' => 'PAY_FEATURED_ADV', 'VALUE' => '0'),
array ('ID' => 'PAY_RECPR', 'VALUE' => '0'),

Now rerun the installer by pointing the browser to /install/index.php. You might have to put that file back if you removed it or renamed it. You should also set the writing permissions of /include/config.php.
Now that the new fields are added to the database, remove the install script.

2. in admin/conf_options.php

FIND:

array ('ID'            => 'PAY_NORMAL',
         'NAME'          => _L('Regular price'),
         'DESCRIPTION'   => _L('Unit price for regular links...'),
         'CONFIG_GROUP'  => '9',
         'TYPE'          => 'NUM',
         'REQUIRED'      => '1'),
array ('ID'            => 'PAY_FEATURED',
         'NAME'          => _L('Featured price'),
         'DESCRIPTION'   => _L('Unit price for featured links...'),
          'CONFIG_GROUP'  => '9',
          'TYPE'          => 'NUM',
          'REQUIRED'      => '1'),

REPLACE BY:

array ('ID'            => 'PAY_NORMAL_ADV',
         'NAME'          => _L('Regular price +'),
         'DESCRIPTION'   => _L('Unit price for regular links+ ...'),
         'CONFIG_GROUP'  => '9',
         'TYPE'          => 'NUM',
         'REQUIRED'      => '1'),
array ('ID'            => 'PAY_FEATURED_ADV',
         'NAME'          => _L('Featured price +'),
         'DESCRIPTION'   => _L('Unit price for featured links+ ...'),
         'CONFIG_GROUP'  => '9',
         'TYPE'          => 'NUM',
         'REQUIRED'      => '1'),
array ('ID'            => 'PAY_NORMAL',
         'NAME'          => _L('Regular price'),
         'DESCRIPTION'   => _L('Unit price for regular links...'),
         'CONFIG_GROUP'  => '9',
         'TYPE'          => 'NUM',
         'REQUIRED'      => '1'),
array ('ID'            => 'PAY_FEATURED',
         'NAME'          => _L('Featured price'),
         'DESCRIPTION'   => _L('Unit price for featured links...'),
         'CONFIG_GROUP'  => '9',
         'TYPE'          => 'NUM',
         'REQUIRED'      => '1'),

3. in submit.php

FIND:

if (FTR_ENABLE == 1 && PAY_FEATURED > 0)
      $price['featured'] = PAY_FEATURED;
   if (PAY_NORMAL > 0)
   {
      $price['normal'] = PAY_NORMAL;
      if (PAY_ENABLE_FREE)
         $price['free'] = 0;
   }

REPLACE BY:

if (FTR_ENABLE == 1 && PAY_FEATURED > 0)
      $price['featured'] = PAY_FEATURED;
  
   if (FTR_ENABLE == 1 && PAY_FEATURED_ADV > 0)
      $price['featured_adv'] = PAY_FEATURED_ADV;

   if (PAY_NORMAL > 0)
   {
      $price['normal'] = PAY_NORMAL;
      if (PAY_ENABLE_FREE)
         $price['free'] = 0;
   }
      if (PAY_NORMAL_ADV > 0)
   {
      $price['normal_adv'] = PAY_NORMAL_ADV;
   }

FIND:

switch (strtolower ($link_type))
      {
         case 'free' :
            $data['NOFOLLOW'] = 1;
            break;
         case 'featured' :
            $data['FEATURED'] = 1;
            break;
         default :
            break;
      }

REPLACE BY:

switch (strtolower ($link_type))
      {
         case 'free' :
            $data['NOFOLLOW'] = 1;
            break;
         case 'featured' :
            $data['FEATURED'] = 1;
            break;
         case 'featured_adv' :
            $data['FEATURED'] = 1;
            break;			
         default :
            break;
      }

4. in payment.php

FIND:

if (FTR_ENABLE == '1' && PAY_FEATURED > 0)
   $price[$link_type_int['featured']] = PAY_FEATURED;

if (PAY_NORMAL > 0)
{
   $price[$link_type_int['normal']] = PAY_NORMAL;
   if (PAY_ENABLE_FREE)
      $price[$link_type_int['free']] = 0;
}

REPLACE BY:

if (FTR_ENABLE == '1' && PAY_FEATURED > 0)
   $price[$link_type_int['featured']] = PAY_FEATURED;

if (FTR_ENABLE == '1' && PAY_FEATURED_ADV > 0)
   $price[$link_type_int['featured_adv']] = PAY_FEATURED_ADV;   

if (PAY_NORMAL > 0)
{
   $price[$link_type_int['normal']] = PAY_NORMAL;
   if (PAY_ENABLE_FREE)
      $price[$link_type_int['free']] = 0;
}

if (PAY_NORMAL_ADV > 0)
{
   $price[$link_type_int['normal_adv']] = PAY_NORMAL_ADV;
}

5. in include/constants.php
FIND:

$link_type_int   = array ( 'none' => 0, 'free' => 1, 'normal' => 2,
                        'reciprocal' => 3, 'featured' => 4);
$link_type_str=array ( 0 => _L('None'), 1 => _L('Free'), 2 => _L('Normal'),
                     3 => _L('Reciprocal'), 4 => _L('Featured'));

REPLACE BY:

$link_type_int   = array ( 'none' => 0, 'free' => 1, 'normal' => 2,
              'reciprocal' => 3, 'featured' => 4, 'normal_adv' => 5,
              'featured_adv' => 6);
$link_type_str   = array ( 0 => _L('None'), 1 => _L('Free'),
                  2 => _L('Normal'), 3 => _L('Reciprocal'),
                  4 => _L('Featured'), 5 => _L('Normal+'),
                  6 => _L('Featured+'));

6. in include/functions.php
FIND:

function determine_link_type($type = 0)
{
   if (!preg_match ('`^[\d]+$`', $type))
      return false;

   $type = ($type < 0 || $type > 6 ? 0 : intval ($type));

   switch ($type) {
      case 4  :
         $return = 'featured';
         break;
      case 3  :
         $return = 'reciprocal';
         break;
      case 2  :
         $return = 'normal';
         break;
      case 1  :
         $return = 'free';
         break;
      case 0  :
      default :
         $return = 'none';
         break;
   }

   return (!empty ($return) ? $return : false);
}

REPLACE BY

function determine_link_type($type = 0)
{
   if (!preg_match ('`^[\d]+$`', $type))
      return false;

   $type = ($type < 0 || $type > 6 ? 0 : intval ($type));

   switch ($type) {
      case 6  :
         $return = 'featured_adv';
         break;
      case 5  :
         $return = 'normal_adv';
         break;
      case 4  :
         $return = 'featured';
         break;
      case 3  :
         $return = 'reciprocal';
         break;
      case 2  :
         $return = 'normal';
         break;
      case 1  :
         $return = 'free';
         break;
      case 0  :
      default :
         $return = 'none';
         break;
   }

   return (!empty ($return) ? $return : false);
}

We are almost done, we only need to modify the submit form to show the additional payment plans.

in submit.tpl
FIND

{if $price.featured}

ABOVE that, ADD:

{if $price.featured_adv}
<tr><td>
<input type="radio" name="LINK_TYPE" value="featured_adv"
            {if $LINK_TYPE eq 'featured_adv'}checked="true"{/if}>
            {l}Featured links +{/l}
</td><td>
{$smarty.const.HTML_CURRENCY_CODE}{$price.featured_adv}
</td>
</tr>
{/if}

FIND

{if $price.normal gt 0}

ABOVE that, ADD:

{if $price.normal_adv gt 0}
<tr>
   <td><input type="radio" name="LINK_TYPE" value="normal_adv"
         {if $LINK_TYPE eq 'normal_adv'}checked="true"{/if}>
         {l}Regular links +{/l}
   </td>
   <td>{$smarty.const.HTML_CURRENCY_CODE}{$price.normal_adv}
   </td>
</tr>
{/if}

You are done! If you are combining this with the deep links mod, you should place onclick="regular();";, onclick="featured();";, onclick="no_deeplinks();"; in the appropriate radio buttons.
Below is the javascript needed

{literal}
<script language="JavaScript">
function setVisibility(id, visibility) {
document.getElementById(id).style.display = visibility;
}
function featured(){
setVisibility('field1_title', '');
setVisibility('field1_url', '');
setVisibility('field2_title', '');
setVisibility('field2_url', '');
setVisibility('field3_title', '');
setVisibility('field3_url', '');
setVisibility('field4_title', '');
setVisibility('field4_url', '');
setVisibility('field5_title', '');
setVisibility('field5_url', '');
}
function regular(){
setVisibility('field1_title', '');
setVisibility('field1_url', '');
setVisibility('field2_title', '');
setVisibility('field2_url', '');
setVisibility('field3_title', '');
setVisibility('field3_url', '');
setVisibility('field4_title', 'none');
setVisibility('field4_url', 'none');
setVisibility('field5_title', 'none');
setVisibility('field5_url', 'none');
}
function no_deeplinks(){
setVisibility('field1_title', 'none');
setVisibility('field1_url', 'none');
setVisibility('field2_title', 'none');
setVisibility('field2_url', 'none');
setVisibility('field3_title', 'none');
setVisibility('field3_url', 'none');
setVisibility('field4_title', 'none');
setVisibility('field4_url', 'none');
setVisibility('field5_title', 'none');
setVisibility('field5_url', 'none');
}
</script> 
{/literal}

Please refer to the deep links mod for more details on this. fieldX_title and fieldX_url are the ids of the rows corresponding the deep links fields, as explained in the deeplinks mod.