The sog field pup is a really fine low cost knife. Just don't buy it with the mock leather sheath, which is crap.

Someone mentioned the kabar dozier folder. I think there are two different lines of kabar doziers. The lower cost folders can be gotten for under $20, including shipping, on ebay. They are good, lightweight (2oz), lockback knives. you can spend a lot more money for less knife. It's what I use when camping/hiking in the northeast.