Are ya lookin' for traditional or inline?

I'm not familiar with the inline guns, so can't speak for which have proven troublesome.
With the traditionals, stay away from the cheapest imports. The locks on them aren't well made and the barrels won't withstand Reasonably high pressures.
Care and feeding of the traditional is pretty much the same regardless of make or model. With a $500 budget you should be able to pick up a good used T/C or CVA along with plenty of the necessities to feed and care for it.

"There are three kinds of men
Those who learn by reading
The few who learn by observing
The rest have to pee on the
electric fence and find out
for themselves."