1. That he has money to pay. 2. That he will pay the money he's ordered to pay. 3. That he will pay that money in a timely fashion.
Bottom-line, this person is not going to give you a product that you're happy with and definitely not on the timeframe you need. Go ahead and file a small-claims case against the person but count the money gone.
There's lots of good advice on here about what to do, raise the cash again, hire a good programmer using the advice given above and below this and move on. Don't waste any more time pleading, threatening, or talking to this guy. Sue him and put it in the past, count the money gone. If you ever get any of it back, apply it to something different, server costs, etc.
Honestly? $2,500 is a very, very cheap price to pay for everything you've learned here. Learn from it and how to avoid this situation in the future (plan out all contingencies ON PAPER with the person ahead of time.)
I beg to differ. As an entrepreneur, this path would cost time and money. $2500 can't be such a big deal. Also, you'll never get support for the code by anybody else. As a programmer, I'd never work for anybody who sued a fellow programmer over disagreements (only possible case for excuse of this: trojan inside the code or backdoor.) You are part responsible because you hired the programmer,
Next time perhaps you should use a site like rentacoder, elance, or topcoder. And learn first how people use it, it is a tool to help you out, not a one-click solution.