OP, there are deals to be had in the used market as well as new. I am not one to tell you how to spend your money because I'm not the one making it. I had to go used for my first bike and I got a nice bike. My budget was $600 TOTAL. I didn't have a helmet, pump, or anything to get me going so I was forced to go used. Everyone will in fact have a different experience. I try to be completely realistic in my thinking. You set a $500 budget for a reason and that's the big picture here. If you can wait, then by all means wait a couple months and save another 2-3 hundred.

There are deals out there, here is an example. This is on the small side for you but it shows you what you can get if you look,

$450 obo Specialized Allez road bike 2012 model