If you're buying one that hasn't had a top end rebuild keep a few K saved for the inevitable job. I bought my 3.2GT with 55k on the clock and the gaskets had failed.
Rust, welding sills can be expensive check these. Rear shocks fail at spring pan, if original these will need replacing.
Clutch and cambelt is an expensive job, factor these into the purchase.
I would buy one that has had a top end rebuild and wizard manifolds fitted, ideally with a queef/Q2.
They are lovely cars and a good way to get a GTA without paying 13k+
156 2.5 V6- awaiting suspension and brake upgrades!!
GT 3.2 wizard cat back, wizard manifolds, full head rebuild, quaife, KW coilovers, full respray