I use machines made by (L&R) and (Dentronics)
I have three that range from 2.5 gallons up to 3.5 gallons.
All three of them have been purchased used, one of them purchased in non-working condition which I repaired easily and have been using for more than 5 years (I have about $50 into that one)
I suggest you get a cleaner with a tank capacity to fully submerge the entire carb body and measure at least 1 inch below the top ridge of the tank.
I don't like to keep the fluid close to the upper lipe of the tank because it spills and spalshes all over....the lids just sit on the tank top, they are not sealed.
There are many places to find untrasonic cleaners being auctioned so go web searching and see what you can find.
Also, get in touch with your dentist and see what they recommend, they often have insights into sales you will never hear about from other dentists.
Don't be afraid of older units either, the kind with a detached tank and power generator connected via a special cable. They often get tossed aside for being too old to pass some typeof health and dafety requirement but in working order they are just fine.
When looking at older units look closely at the tank thickness and wear.
Lots of these are used with stuff just tossed into the tank and this wears the bottom of the tank thin.
If there is a drain tube grab that and gently wiggle it around to watch the tank bottom flex.
Stay away if it has worn thin unless the price is very low.
Looks for signs of leakage, which are often hard to distinguish from spillage, but still, look.
There are good used machines out there for the taking if you look often and stay patient.
I would bet you can find a good used industrial machine for about $300 or less.
If you get stuck get ahold of me.
You can send your baseplate, and the rest of the torn down carb, to me and I'll sonic clean it for you. You just have to pay for shipping.
Have a great day.