I think $400 is good for a relatively intact and working T2 machine. I don't think it has to be pristine but the cabinet should be solid, the guns working, the monitor still going strong, and the side art in at least "good" condition
I just picked up a T2 machine that's stuck in diagnostic mode for $120. Cab has definitely seen some use in an arcade. I'm going to clean up all the grime/cobwebs and start working on the wiring harness so i can get it out of diagnostic mode (start buttons aren't connected right for one so that'll probably get it out of diagnostic mode

). The side art is in good shape except for where the mdf was chipped along some of the edges. I'll probably try and bondo it and color match the paint to the side art (i'm hoping to save it rather than spend for some reproduction or NOS stuff). It also needs some touch up paint on the black parts and new t-molding.
This will definitely be a labor of love for me since this particular cab is in my top 5 must own arcade games list.