I just bought one via ebay, was not "cheap" as such but cheaper than MRRP so....
It depends how much/big things you want to clean, I got one big enough to handle a couple of stripped first stage regs (bigger than a jewelry cleaner, smaller than a industrial one)
From my brief and no doubt inaccurate research the small plasticy "home" units for jewelry and suchlike go from £10-£30, Tattoist, small dentistry and light duty stainless trayed ones go from £40-80 and then the heavy duty ones come in from about £90 upwards to hundreds if not thousands...
I got one with a stainless try, 1.4ltr capacity, digital timer, basket for the bits to be cleaned and it was light industrial use (jewelry shops, dentists, tattoists etc) so designed to be used for extended periods, think its got a fan or something to keep the gubbins cool rather than relying on you only using it for a few minutes!
. Was brand new off ebay for less than £70, should be more than I need.
Do abit of digging and remember to google things by part number off of ebay before bidding, I found reviews and a manual for mine on a US site and it convinced me it'd do what I wanted.
Happy hunting,
BEN
UPDATE- So my Ultrasonic cleaner has arrived, I tried it last night on a few household items with an impressive degree of success. Tonight I have a misused and abused Argon reg thats going in the cleaner, I have high hopes for it
FWIW I got it from-
http://stores.ebay.co.uk/CLARK-OPTICAL they seem like a fair bunch of people and offer a reasonable selection.
BEN