Proposal, Pricing and Concept request for shopping site

Requirements:
1. Buy and Sell: User can Buy and Sell Like in [hidden] , [hidden]
2. User account : User can create an account , Post an Item , any products ,
3. User Post pictures of the items
4. Categories of products , used items , like in eBay
5. Pay Pal Integration like in eBay , [hidden] other related sites out there
6. User management
7. Clean design like [hidden] , [hidden] , not messy like eBay

Please Provide
a. Concept
b. Pricing
c. Time Frame : Start to finish
d. What platform or programming language to use