fix heavily modded oscommerce site

I am looking for a developer who can fix several problems in a heavily modded oscommerce site thanks to the previous GAF developer who took the money and ran after these issues were uncovered a few weeks later (tosser!): Here are the issues: 1) in back-end control panel when changing shipping cost for a particular manufacturer to 0.00 the front-end checkout fails to move to payment page when clicking next (please note this is a modified shipping module which can set different costs per manufacturer) 2) an HSBC payment module was installed which allows customers to place orders and make payment via HSBC secure gateway. Emails which detail the order are sent to store owner and customer and manufacturer.....but from time to time a payment is taken with no orders being registered in the site or emails sent. 3) price matrix tables (a custom mod) are entered in the back-end of the site which allows products to be sold based on size (H x W). For some reason the existing ones work fine but any new ones do not work. I assume some sort of corruption has occurred. Please provide me with quotes...payment will be made 15 days after job is complete to allow testing.