I sent you a PM. I would like to discuss options, do some research and planning with you. I don't believe the project will cost $50,000. The project will probably take 6-12 months to work correctly, we will need to look into some caching options, research the best optimised database queries and look into some frameworks to build upon.
I can be hired for 12 months at $36,000 with a one on one service.