What kind of benchrest? The two piece 3 or 4 leg forearm rest with (usually) sand filled bag under the belly of the stock or the one piece jobs that you rest your entire rifle on?
IMO, for the two piece set-ups, The Rock from Caldwell (Battenfeld Tech) is a good bargin for slightly more serious shooters. Has the weight for stability, pointed feet to help reduce shifting of the entire rest, forearm stop, adjustable wings for a better fit of the sand filled bag, etc. The basics of the more serious rests. There are, of course, the heavy duty hardcore rests with micro adjustments, more adjustments, more weight, etc. but they normally cost 3-5 times as much as The Rock. If you're looking to get anything close to the best, expect to pay at least $300. If you're looking for just a very stable platform to zero scopes and do rudimentary groups, can't beat the Caldwell offerring. IIRC, I think I paid ~$70 from Sportsman's Guide but don't think they have any at the moment. Midway has them for $69 (C&R) / $75 (non-C&R). Caldwell has another offerring called The Handy that doesn't, at least to me, look very good. Made out of plastic (=too light).
If you want to go cheap, Caldwell's Dead Shot front and rear sandbags work OK. ~$13-$15, you supply the sand. Not as stable but gets the job of sighting in done.