The guys at Sam Ash said they're usually $300 new for the rack unit. More like ~$440. It takes a 9vAC 900mA minimum adapter... I found a few online, USR makes a 1000mA 9vAC adapter, I'm assuming that it means 9v RMS, having little experience with AC power adapters. Also, I'm not sure if a US Robotics adapter will create ungodly amounts of noise in the signal or not. I shot an Email over to the chaps at iSP, asking if I could buy a replacement from them, but I haven't heard back from them.
I figure buying a ProrackG for so cheap means I'm entitled to some obstacles to using it.
EDIT: The Digitech Whammy and most of the RP-series boards use the same adapter style, 9vAC at 900+mA... I assume those would work just as well?
Just call them. I emailed them about some stuff and got no response, but once I got them on the phone they were very helpful.