You can probably find a lot of lonerlocks that can be unscrewed easy enough. One warning though, for some reason a lot of the Smith and Wessons have cheap screws that mash up when you try to take them apart, so you might be disappointed there.
A lot of the CRKT linerlocks can be completely disassembled, and as a bonus they will have a LAWKS mechanism added that you can look at. They will cost more than an M-Tech, but some of them might have better steel (not all of them unfortunately) so you can reassemble it and have a knife to actually use. See if you can find one for $30. They usually look like the parts fit together better that cheaper stuff.
The Gerber Air Ranger is now discontinued. At $45 for a knife from Taiwan, it was a little too espensive. But Gerber or some wholesalers must have dumped them cheap, because you can hurry and grab one for about $20 on clearance right now from various ebay sellers. It's a pretty darn nice knife for $20. (Edit: forgot to specify this is a linerlock, with the liner nicely set into one of the handle slabs)
The CRKT Moskeeter is a lockback with a screw together pivot, so you can remove the blade and rotate the lock bar enough to see it, but the handle doesn't come apart. The fair market price is $15 or less.
Kabar is making some cheap Dozier models right now. Lockbacks, AUS8 blades of a few different shapes, and Zytel handle. Same deal as with the Moskeeter. You can remove the blade and look inside, but the handle is molded together. About $20.
Bear MGC (or maybe it's just Bear now) has a few lockbacks for $20 or less that don't come apart but have clear handles so you can see what it looks like inside. You can probably see how the spring is mounted too, which won't be as visible with others.
The current Spyderco Delica is molded and pressed together so it can't come apart, but sometime in the near future the replacement model will be all screws, so you can disassemble it completely if you want to do it with a quality knife ($40-50).
