Just picked up a Rush 2049 last weekend, myself. (Woohoo!!) Got a single unit for $350, everything works, just needs some contact cleaner on a few bits and a general scrub down. I think I got a great deal.
As for the regular SF Rush's, they're getting pretty cheap. I passed on a pair of Rush the Rocks(sequel to SF Rush, but same cabs and everything) for $800 not too long ago and last I knew, they were still for sale. I live in a town that is very cutthroat for good arcade game/pinball deals. If there's a bargain to be had on CL, it's gone in a few minutes. Both of those Rush the Rock's were all original units in fantastic shape, too. The main reason I didn't buy them is because they're not upgradeable to the 2049 game series. From what I understand, the green Rush's can do SF Rush and Rush the Rock(Alcatraz edition) and the Rush 2049's can do 2049, 2049 Tournament Edition, 2049 Special Edition.
I really wish someone could come up with an emulator or new main CPU that can switch between and play all of the games in the series. They all use the same hardware for the most part, seems like it should be doable.