Complex Freelance type Ecommerce site

I am looking for good, efficient, and preferably people with decent English skills for this project. I am going to explain the project in as much detail without giving the idea away. I have the design already made so please only give me SERIOUS quotes for the coding. Basically when one comes to my site they can either buy or sell items. Therefore there needs to be one account; not a separate login for buyers or sellers. On the sellers end they will be allowed to upload their own products to the inventory of my site. They can set their own price, details, etc. When buyers come to my site they can view the inventory and if they choose to buy a product they will pay via our merchant account or Paypal and the item will digitally delivered to them Now for the tricky part in regards to coding, there are some complications. Being the fact that I am going to have thousand or even tens of thousands items in my inventory there needs to be a very intricate search feature. There will be a basic search and advanced search which I will go into more detail with. Now since the items on my site are created by the sellers themselves; every time someone purchases that sellers product they receive 80% of the cost which gets debited to their account and they will essentially have a number in virtual dollars in which they can withdraw or use to buy other notes. I need this project started immediately and I am looking for a long term relationship. I have attached a document better displaying the database scheme. I need this project started very soon. Please get back to me.