Australian TNT Shipping Calculator for WP-Ecommerce Needed

Project Description:
I have a functional ecommerce site using Wordpress combined with WP-Ecommerce and payment processing done via PayPal web standards.

There are currently 25 products in the store and this will grow in the near future.

I'm looking for someone to build functionality into the WP-Ecommerce(WPEC) plugin that enables TNT shipping to be calculated in Australia.

Shipping Calculator - Option 1 Using TNT Servers
I have from TNT an XML schema enabling someone who knows their way around WPEC to collect the information they need, pass it to TNT servers (will need to be server side tech) and return a shipping cost for the products. This will then be added to the total cart price before being sent to Paypal.

Shipping Calculator - Option 2 Using Internal Calculators
I have full details of the shipping costs from TNT.
To give an idea of the scope of work: -
You will need to convert a postcode entered by the user to an area as defined by TNT.
Each area (there are around 95) has a basic cost, price per kilo and minimum cost. Some items have to have a flat fee added to this calculation. The shipping cost is
(product weight X rate per kilo)+ Basic (+conditional $15)= Cost
This cost has to be checked against the minimum cost for that product.
After that the total shipping costs for all products need to be totalled before sending through to Paypal.

Please tell me if you have experience working with WPEC as it's poorly documented.

Please come back with bid and estimated time to complete! :)