I picked up a pro grade ultrasonic cleaner with heater element at a flea market. I only paid $5 for it, and it has worked out great.
I can leave a couple of crusty locks in the tank overnight, and in the morning after a shot of good lube they are very useable.
This works so well not only because of a good deep cleaning, it also flushes out most of the crud. The solvent becomes very muddy.
This has added a lot of locks to my collection, at very little cost.
Regards
Buzzzy