Price depends a lot on your location, how willing you are to tolerate some issues, and your luck. The last truck I bought was $150 for a 4x4 and it just needed a head and a new paint job. Years before that I paid $500 for a 4x4 that was a complete basket case with wiring, motor, and body issues.
The main bad is rust. Everything else pales in comparison to repairing rusted out parts of the cab. Pay special attention to the rocker panels right under the door and the floor boards. Surface rust isn't too bad to deal with if you are looking to paint anyway, but stay away from bubbly holes and cracks.
Another common problem is badly cracked dashes so on that just look for something that doesn't have big chunks out of it or curling up. You can get a formed dash cap that covers the top 1/4 to 1/3 of the dash for under $100 now, or coming soon a ~$400 full replacement. (see old threads here for info on the replacement). Don't expect to find a perfect dash, but if you do that would be a big plus.
Motors have a low tolerance to overheating which leads to warped heads and/or blown head gaskets. Make sure you get it fully up to temp on the test drive and look for traces of leaks between the head and the block. The most common place I've spotted them is on the drivers side right behind the exhaust manifold. Look for traces of white flaky residue from water leaking out. Its not too hard to replace the head gasket so that might be a good way to get a cheap "fixer" truck that is otherwise in good shape.
Depending on where you live and local smog laws there are some stock motor upgrades that would be nice to have come with the truck. A header and a Weber carb being the top two. A custom reground cam would be nice, but tough to actually check for when purchasing.
In general, pick solid body over perfect mechanical. You can drop a lot into fixing a motor, trans, or other mechanical parts but if you've got rust in the body or worse the frame you'll never stop paying for it.
I'm not a fan of lowered, so not the person to comment on that.

My 77 2WD is dropped about 1/2" to 1" in the front and stock in the back. It still rides nice, doesn't leave metal behind on speedbumps, and handles like its on rails.