It just quit mid cycle about 2 days ago and I can't figure out what's wrong. I've changed the door switch, cleaned out all the lint, vacuumed out the thing as best I can, tested every wire and fuse I can reach... but it still won't turn on again, checked the fuse, power cord and where the cord plugs into the wall. Am I just out of luck and need to just buy a new machine, or will it be worth at least $70 to have a repair man come look at it?

It's dirty and lint deposits have built up, as it always does, in all the air ducts. A little vacuuming out does nothing. You will have to take it apart and test the thermal fuse near the heating element and the heating element, but it may be resettable. You will have to clean the drier out thoroughly or it is all for nothing. Every air duct will have to be removed and scraped and washed out to remove baked on lint deposits which is like a concrete lining. This will burn so the manufacturer has installed the safeties to keep from having a house fire. The safeties are oval-shaped with a round center part containing the safety with two plug-on terminals for the wires and when they burn open, from the dryer being dirty, nothing will work. Using an ohm meter you put a lead on each terminal of the safety, with one wire unplugged, and if it's good you will have a reading of about zero; if it's bad it will read infinity. Driers were the number one cause of fires at one time, hence now we have safety fuses. Look at: http://www.youtube.com/watch?v=MMP7BW1lLs4 to see how. Also: http://www.youtube.com/watch?v=iBiRw-KElC4 ; http://www.youtube.com/watch?v=yFTZGgVisCI
http://www.electrical-forensics.com/Dryer/ElectricClothesDryers.html
http://fixitnow.com/wp/2010/10/09/whirlpool-dryer-model-le5800xsw3-wiring-diagram/
When you finish cleaning the drier and install a new safety it is best to also replace the belt, too, because you do not want to have to disassemble it all over again and if the belt is over two years old you should replace it.

Note that on most of the videos it does not show them washing out the parts, but this is important because it's the only way to really get the parts clean, just don't get motor wet or the capacitor if it has one. Vacuum out the motor to remove all dust. I would move the drier out to your garage to have plenty of space to work. You also want to check your vent and clean it, also. The vent should have a short run and be straight as possible. The job is really easier than it sounds. There is no shortcut that will work; it has to be cleaned well. Before you re-assemble it make sure to use white lithium grease (high-temp grease) and grease all bearings. Just vacuuming out the dryer a little does little good. DrTom4444