Design & build a new shopping website by modifying Joomla , Virtual mart

We need to build a shopping website with ten of thousands of products, tens of sub categories, with variety of payment modes, variety of shipping mode, with affliate system, gift function, discount voucher system, reseller system . and most importantly can upload , edit products very very fast. We have seen Joomla-virtual mart, we think to modify from Joola-virtualmart is easier and cheaper to do. Detail : [login to view URL] budget is USD300 ( never ask extra when bidding or after awarding ) 2. your promises in PMB will be our agreement, and all your reply and promises MUST be within Budget of USD300. 3. Tell me how many modification (from default joomla-virtualmart)you can provide, included big and small modifications. Pls provide more detail so that we don't have to argue in future. I will most likely award the bidder can do most modification because i cannot think of all the modifications i need before we start. I can only think when we go along . 4. tell me how much time of "after support" you can provide , and tell me how much fund BUYER can keep during this promised period. 5. Provider will be given a hosting and a domain name (testing) to work on. But Provider need to change the testing domain to our existing store domain and make it go live. ( the day we go live with my store domain will be the *completion day) 6. Buyer will only release fund after 90days from *completion day (for inspection). 7. Only for Provider who is willing to carry out this job for long period like up to 6 months, because BUYER is very busy, maybe only can tell you one modification per day, as well as inspect your done modification one in a day. You may take other project, but spare a little time everyday to work on my project.