-Benchmade Sibert 755 MPR, M390 Super Steel, less than 3" blade, $140 on eBay.
-Spyderco Paramilitary 2, S30V, 3 7/16 inches, $110 preorder from dealers.
-Spyderco Gayle Bradley, CPM-M4, 3 7/16 inches, $140.
-Zero Tolerance 0350CB, Elmax Composite, 3 1/4 inches, $140.
I personally think the Gayle Bradley is the best value, with the only true downside being that the blade can rust easily(depends on how much he sweats). But it typically has the best edge retention of most steels. And with carbon fiber handles, it's definitely a good value for the price.
The Paramilitary 2 is the hottest knife Spyderco has at the moment. It is constantly sold out in most places and typically sells for a good $30-$40 more than the preorder price on eBay. Ergonomics are pretty close to perfect. That aside however, I find S30V to be "last year's" steel.
The Benchmade 755 MPR sports the all new M390 "Super Steel", and IMO it rightly deserves to be called that. The steel is far superior to S30V in edge retention. The handles are G10 with a titanium monolock. Impressive value for the price, though it's typically cheaper on the secondary market rather than a dealer. The thing that might get you is that the blade is just under 3 inches and is extremely THICK. It's not meant for cutting through thick mediums like styrofoam or wood, though seatbelts shouldn't be a problem. It's quite a short folder, but the handles are a good half an inch thick. I don't have much of a problem carrying it inside my pocket(not clipped) at work though(standard black work pants).
The Zero Tolerance 0350CB is a smaller version of the 0300 series. I consider it a midsized EDC. Elmax is IMO, a tougher but slightly less wear resistant version of S30V. Personally I found it to be a tad small for my needs(though not smaller than the 755 MPR).
As far as defensive use goes, any knife with a good grip and belly for slicing will fit the criteria. But unless either you or your father sharpens the knife regularly, having a premium steel might be a waste. At least, that would be my experience. Having a steel with better edge retention would seem to make sense, especially for people who don't maintain their edges. But having to pay an additional $40-$80 just for that doesn't seem worth it to me.