I used Ultrasonic a lot. Yes, it is invaluable for cleaning lots of stuff.
When my good "professional model" burned out early last year, and I couldn't afford to actually replace it, I bought one of these to "see me through" until I could afford a good one:
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=3305
I wasn't expecting much out of it, and it was smaller than I wanted, but it ended up working better than I expected.
If you are doing small enough stuff and don't need heavy duty, continuous use, it ought to do. They are regularly on sale for $29.95 each, and I have bought a couple of more since the first (which is still working just fine.)
Here is a little tip: for multi-purpose cleaning solvent you can use "Formula 409" or "Fantastic" or save even more money and buy the 1 gallon generic "cleaner-degreaser" at Costco. It is a LOT cheaper than the special ultrasonic cleaner solutions, and works as well if not better.