If I was going to buy a used bow it would be an Elite. Their warranty is transferable plus they are the only one that will over night you a bow if you happen to break yours on a hunt. It is called the Hunter Guarantee. I won't buy a used bow if the warranty is not transferable. But like everyone else has stated you probably would be better trying to look at last years models especially after the ATA show. I shoot an Elite Energy 35 and love it but here are a few nice bows for under $500. I would write these down and call your nearest pro shop and see if they have them so you can shoot them. Compare the prices online to what the shop has because some shops might match the price if it is cheaper online.
Hoyt Powermax
Mission Archery
Quest Amp, Forge Quest is made by G5
Bowtech Fuel, Assasain
Diamond
PSE Bow Madness 30