Camillus also has some good ones. I have always liked Camillus even though the quality can be hit and miss. I have gone through a couple of their marlinspike folders. Both broke the backspring on the marlinspike after about a year, but for the price it’s still a good deal. Marlinspike knives only come in two flavors- cheap and very expensive. I tend to drop things in the water on the regular, so a cheapy serves me well. If I ever get around to making my own it will definitely have a lanyard attached when I’m on the water.
Gonna second the Opinels...grew up on them. making my own version right now (won't be under $50...lol. hoping to keep it in the $85 range) My boy's first knives were opinels...light, strong, great steel, sharp from factory, simple enough for a kid to use....They are simply a great knife. I also have a Cold Steel twist-master that is their take on the Opinel....not a "looker" but a very good knife also.
SRM (SanRenMu) 9201. It supposedly has a D2 steel blade, and the "axis" lock is nice. My only real complaint with it is that the pivot loosens up quite a bit, but I just haven't tracked down my tube of thread locker yet to fix it. The edge seems to hold up so far, and for $30, it's more/less exceeded my initial expectations.