To be honest, 3k isn't gonna find you much of a get in and drive machine. Will need work somewhere on it. But then again, u may find a bargain at 3-3.5k which really is in good nick. Not many out there though.
As for rust they go everywhere, and the Bodykit hides it all. Back arches go, giveaway is bodykit crinkled over the arch. Outer and inner sills rot and spreads to near by floorpans.

Both rear valance joins rot, check the seams aint smoothed over with filler, and the lip rusts cos of lack of paint.

Get under the boot floor check around rear spring mounts, they can go, also check the back chassis rails, runs along boot floor, check for fresh underseal covering the rust up.

Moving forward, open sunroof, and check condition of pan, rust will be around drain holes, the covered seam running right the way round, and back in behind the runners, lot of rust can be in here.

Check around windows and rubbers for rust creeping out from under the rubbers, means the seam under there has had it. Now under the bonnet> battery tray, always goes on most, where the water sits around the tray, look for any plates welded in or bad repairs.

Also look on the back edge of the wing seams, (underside) rust can start here and spread to the inner wings, check all condition of the inner and outer wings can be rotten.

Now check Cross member, usually destroy'd with rust and front valance on all the joins and behind headlights.

Thats a brief of what to look out for, otherwise id be here all night, sure theres more.