So if we were planning on having a 1 year lease I'd be screwed? So he says "we couldn't agree to terms" and then the judge says "why did you write him a check if you didn't agree to terms right?" and what does he say?
What are you going to say if he argues that you guys were still negotiating, and that the money was as a deposit that you promised to give back if you couldn't reach terms?
It's a crappy situation, but hopefully the lesson learned is that *every* real estate transaction should be in writing, always. You may be able to recover a month's rent, you may be able to recover your actual documented expenses, or you may be able to recover nothing (as, as mentioned above, there is no evidence that somebody else was going to rent the place). A lot will depend upon the judge's discretion, and what s/he thinks your detrimental reliance was.
In a nutshell, my prediction is that the judge is going to say "forget about the contract, there was no contract. There was no lease. Now, how did you rely upon this guy's promise, and what were your actual damages?" That may or may not be tough to prove, depending upon how lenient the judge is.
Also, of course, as others have said, there's a duty to mitigate. Make sure you get the fliers / advertisements up again as soon as possible, and start showing it to tenants again.