is the power steering pump expensive to replace?Like anything these days, brand new aftermarket, say $500 tax in. But it may be replaced already. Anyways, I would not let that hold you back. It seemed like GM used the same type pump from 1996 thru and including 2002 and they would be in other GM units as well. Probably out of a wrecker they would run $50. I don't think it would be more than a few hours labour at a small shop.
If it's a Limited it would be a bonus because the seats would be much more comfortable. THey are a big car so they have some safety to them. Seat belts are crap though, but that's just my opinion.

They are attached to the top of the seat back and not the B pillar. A GM trade mark.

It's all about the price and condition. Lots of old ppl bought those and as such most are not abused.