If you want easy to replace, then you don't want a Busse family knife, I assume.

In that case, I would recommend Ranger Knives, Ready Detachment or RD series, starting with the RD6. 5160 spring steel, 0.25" thick, full flat ground, very tough stuff. Not the most pretty knives around, and not scalpels, but if you want a knife that you can really pound on and don't want to pay top dollar for it, Ranger Knives is what you want. As a plus, you get to deal with Justin, the owner of Ranger Knives, who is easily one of the most pleasant guys in the business that I've ever dealt with.
There is no such thing as a folding "hard use" knife. Sure, one may advertise a folder as tough, one may call it a hard use knife, and slap a 1/2" thick spine on it, but it will still be a folder, and inherently prone to failure and weakness. Anyone thinking that a folder will actually consistently stand up to really hard use (in the sense that might be called abusive) is kidding themselves.