Durable folders with secure locks in your price range:
Many from Kershaw
A few from Spyderco
AG Russell Featherlite
Seems to me you simply need to browse the selection at a couple of major knife retailers, pick out a few that interest you aesthetically and offer a blade shape and steel that suits you, then search the forum for reviews of those knives.
How about a Kershaw JYD II, Kershaw Lahar, Benchmade Grip, or a Spyderco Endura. I am sure there are more like a Cold Steel Voyager, ect. but there are several good ones. The things you need to look at are blade style, how long you want the blade to be, type of handles, locking style, and I am sure there are other things to consider. GOOD LUCK! Kevin
Yet another recommendation: check the Boker Plus M-type, it's the bigger brother of the highly regarded Trance and Subcom knifes. A solidly made framelock folder that you can buy incl shipping within your budget.