As Ben Cole noted, Harbor Freight has a $39.99 (sometimes $29.) Ultrasonic machine that works VERY well. The identical machine can be found on eBay and Amazon (where I got mine) for $29.-$39. under the brand GemOro. Or just Google it.
Having been in the Jewelry Industry for 30+ years using a $200+ machine I was very pleased with the results I got using this one. The only issue I have with it is that the timer is set for 3 minutes so you have to keep turning it on if parts are not clean the first go round. Of Note: DO NOT USE Ammonia based cleaners on Alloy parts as it may haze them and you will have to spend more time polishing. Start with HOT tap water and the cleaning solution of choice. I use Dawn or Orange Clean among others in a small amount, mixed with the hot water. You DO NOT have to refill the tank for each use. Just change when it gets really dirty.
Jay "happy to have clean parts" Dubiel Halifax, VA USA