Search the threads here about RealVerb. As I recall, a while back Guitar Center (?) was blowing it out at $50 (vs. list price of, um, $299?) - at that price it's an incredible deal. D-Verb is also pretty good (espec. for the price), but IMHO RealVerb is more flexible & natural-sounding (& has a funky pictorial interface that you just gotta love). I believe there's a downloadable trial version at
www.kindofloud.com.
"Native" bundles from Waves & TC|Works also include excellent RTAS reverbs, but you may not consider these "inexpensive".