Price seems pretty good to me.
Obviously, windows will cost at least $100. A decent graphics card will probably run you another $200 or so.
I wouldn't call it low end, though. Other than the GTS 250, it is a pretty nice machine.
People certainly tend to underestimate the first-gen i5s and i7s, honestly the gaming performance between it and, say, a current i5 or i7 would be negligible in the majority of games.
I would say, see if you can get him down to $250. And also see if might have a windows license key lying around, no the one on the side of your desktop or bottom of your laptop will not work.