Rem 40-X in 220 Swift, 22-250, 243 or 25-06 would be great. I'd even look at 6mm.

Depends on his likes/dislikes.

The Savage Tactical is also a great gun, and MUCH cheaper than the 40-X.

I have a friend whose son shoots a 40-X in 220 Swift with a 6-24X Swavorski on it. He can absolutely shoot the lights out at 400. It's sickening. They dabble some out to 600+.

Me, I'd opt for a little bigger bullet at that range for coyotes.