I just picked up a black Rush the Rock Alcatraz in great shape for $500, which I think is a little above or at market value, but it worked perfectly and didn't even need a cap kit.
I bought my first RUSH the rock in "arcade condition" for $600.
Recently, I got one that runs but I had to fix the steering pot and it had a cracked seat and the monitor's blue drive was out. I paid $50 for it. I am almost done restoring it.