Well, most of the boards that I mentioned are in the $400 - $600 range. That's what they go for on e-bay. If you want something that's still being manufactured you'll have to spend a lot more then that.
I'm talking a few grand. From the brand new stuff $500 ain't gonna get you anything cool. Well, may be some of the Roland A stuff. But then you'll have to get an additional sound module if you want sounds.

-ED-