Here's one that looks better -
http://phoenix.craigslist.org/evl/bik/3256024620.html
When you are getting a used bike size is going to be your biggest issue. Finding a used bike in just the right size can be hard - don't believe stuff like what the guy posted in his ad.... a 52cm bike probably is not going to fit such a big range of people (he claims 5'3" to 5"11!)... it's also a little worrisome that he doesn't actually know the size..., but the other ad was a bit worrisome too.
Of course with end of the year sales and such (and you seem to need a good common size) you can probably get into most brand's entry level bikes for about that amount of money or perhaps just a hair more. Check out your local bike shops to see what they've got going for end of summer sales - look for models like the Specialized Dolce, the Giant Avail 5 or the Jamis Satellite Sport. With a new bike, even if it does cost a bit more up front, you may save in the end because you don't have to pay for tune ups or a fitting.