Will it have to endure an environment that would promote rust?
If he is constantly in the water and/or goes diving, then Spyderco's H1 steel is great.
If that's not a huge concern, or it won't be a constant deal..
The Ontario RAT 1 is a great EDC knife. 3.625" AUS-8 steel (Comparable to 440B stainless) blade with a pretty decent heat treat. Comes in at around $30. Not assisted, but it does come in a combo edge and a black blade coating. It's very cost effective, as it takes quite the beating, from what I hear.
Spyderco also has some nice offerings, though for your price range.. with something other than 8Cr13MoV steel, such as Super Blue or VG-10.. you'd end up with something along the lines of a 2" to 3" blade.
Unfortunately, I don't know of many assisted knives, and all of the ones that I do, within your budget, are 8Cr13MoV. For your friend, this steel should be absolutely fine, though.
I have heard some really nice things about the Kershaw Cryo, and Cryo II. Both are nice, thick folders, in the event that your friend either likes them like that or would need it like that. 3.25" 8Cr13MoV hollow-ground blade. Unfortunately, it only really meets one (and a half?) of your requirements, aside from budget. It is an assisted folder, though it only currently comes in a plain edge and gray-colored blade. They go for about $35.
The Cryo is pretty much the same, as far as configurations go. The Cryo is a tiny bit thicker and a bit shorter than the Cryo II, and costs about $30. They are coming out with a "BlackWash" finish, as well, which are currently on pre-order, and would meet two of your requirements, aside from the price.