Bitcoin based auction system

Selected vendor will take an existing open-source auction script (PHPProBid) and modify it to accept Bitcoins as a form of payment. System must allow for payment to seller in the form of bitcoins (as well as a transaction fee to the system in Botcoins per sale). Bitcoins is an peer-to-peer digial currency. You can read more about bitcoins at www.bitcoins.org. I would like to allow sellers to choose which currencies they will accept payment in (Bitcoins being one of the options), as well as shipping methods. The system should have a currency table I that can be updated with exchange rates so the bitcoin price will change dynamically as rates fluctuate. For bitcoin transactions, there will be a bitcoin address that the buyer sends the bitcoins to, and an additional bitcoin address for the system that the transactoin fee will go into. The buyer can also (optionally) specify an address to return bitcoins to in case of a refund. The system will need to confirm the bitcoins. The seller should also be able to indicate how much of payment occurs up front, and how much is held in escrow until the shipment is delivered (bitcoin only). I am open to the vendor's choice of gateway, although I think the most flexible would be JSON-RPC [login to view URL](JSON-RPC) You can find more PHP developer information here: [login to view URL] The website will run under The Onion Network (TOR) so any additional experience there would be helpful.