Customized Classifieds Script

We are in need of a modified classifieds script focused around "wanted to buy", rather than "for sale". It appears that most classified scripts include the basic functionality we need, but a number of modifications would need to be made. The key elements required are as follows; 1. Two levels of paid users... one for the person placing a WTB advertisement and one for suppliers making an offer to sell. 2. Suppliers may submit their priced offers to the buyers, but neither the buyer nor the supplier will be able to see each others contact information. 3. Each WTB ad and supplier offer will need its own discrete listing number for tracking purposes. 4. Each supplier offer submitted to the buyer will need to include an "accept" or "decline" option. 5. If a supplier's offer is accepted by the buyer, payment is to be made through PayPal using their split payment api. Buyer receives payment through PayPal, minus commission.