Polk SDA's pop up for less than that all the time. I got lucky and got a pair of Monitor Audio S6's for 250 and they are very nice. I recently picked up a pair of Klipsch Quartets in Walnut in mint condition for less than that too.
3 very different flavors for less than your 500 budget.
To Me, JBL's are the Vintage speaker to find and I'd look for 3 ways with a 12" woofer
JBL's, Polk's, Dahlquist's, Kef, Mirage, Infinity, are all available....source, room size, and WAF, if you have one, should influence purchase.
The thrill is in the hunt, Good Luck!!