Dave not trying to discourage your friend from buying it not one bit, but alarm bells are ringing in my head by reading your comment.
What I mean is you and him don't work on cars often and maybe not to this extent so don't know what is going to be involved?.
This is my opinion mind but thought I'd give your friend some information of cost lickly involved in getting it good to a1 condition.
With all of that work involved I highly doubt it will cost 3k your probably talking double that, 1st off you said the sills are shot so whole rear quarter got to come off (they go all the way to the roof) and are bonded/fibreglassed/filler so lickly cost to remove/fit kit and full respray after your talking upto 4K depending on body shop.
The biggest and another costly job will be the floors (read mot history on the car it mentions subframe mounts corroded) so brake/fuel lines and other parts will need to be taken off the underside inc engine bay not to mention interior. Then they would need to brace the insides with a X section so no movement will occur and then cut the floor out maybe exhaust tunnel depending on extent of corrosion.
The floor section will need to be done by a professional or at least someone with good experience as this part is crucial in the strength of car, and these people don't come cheap.
As I mentioned already I'm not trying to put your friend off it but half the battle is knowing what your faced with before hand so good luck in what ever your friend decides I'm pretty sure others will voice their opinions too.
