From the pictures, it looks like it might be little to no rust. If it comes with all the parts that were stripped off it, original engine, trans, etc., it would actually be a pretty good deal, if you're handy with a wrench. With so little info, it's hard to tell.
That ad is giving off the vibe of being a disaster transaction- impossible to contact the seller, get information etc.
Those are the type of deals that I never get- I can't ever get decent info so I give up but the next guy has the opposite luck and winds up with a $5000 rust free Boss 351...