I didn't really think to take pics of the undercarriage, but I can say this: to my knowledge, the car is structurally sound and solid. The only areas of rust are in the rear wheel well areas like I showed in the pictures. The passenger side is worse, and I think you can see from the picture of the passenger side that there is a good size hole in the quarter panel. The left-rear lift point is solid, but there is a rust hole behind the right-rear jack point - this is basically an extension of the rust comming down in front of the right-rear tire. The floors aren't an issue - they are completely 100% sold.
How much time/money to fix it? It depends on your skill in this area and the size of your tool collection. If you wanted to restore it 100%, of course you would cut the rust out and weld in new metal from a rust-free junkyard car. Its up to the buyer whether they want to do that, but I'm of the mind that its a nice, clean daily driver, so just buy it for the under- $2,000 pricetag and enjoy it.
Greg