i'd give him $1250. 05 S Works Enduro demo bikes go for ~$1500-$1700.
i wouldn't bother upgrading the rockhopper. it's a good starter bike, but you can get a Stump Jumper with V brakes for $1250. I built one for a customer today and am now thinking about picking one up.(especially since i can get it for ~$700
) You get a lot of bike for the money, especially the +$500 fork. Only thing I'd change would be the levers and maybe a riser bar.
If you buy the enduro have your friend throw in a full tune, and throw some lighter tires on it.(if he hasn't already) The enduro is a really nice bike, especially the S works, but it's a bit too much travel for me. Ask if you can take it for a test ride on a trail.