Minor Changes to Custom WordPress Plugin

Project Description: 
Minor Changes to Custom WordPress Plugin. -We currently have a custom WordPress plugin that was developed to calculate and process monthly teacher fees through paypal. This plugin will work fine for our U.S. based customers, but we need a separate version of it for use on our Australian e-commerce site. Basically, we need the functionality modified in order to work for Australian time and taxes (GST).
 The developer for this project should easily be able to go through the plugin files and understand how it functions and how to further customize it for our Australian site. 
Our site is a WordPress site using: 
-WPMU Blogs MU theme
 -WPMU MarketPress e-commerce plugin
 -WPMU BuddyPress forums plugin
 -Wishlist Member membership plugin

 Programming / Languages
-PHP (WordPress)
 -SQL 
-Javascript (fee-calculator)

 -HTML / CSS