I'd go the cheaper route, for a couple of reasons -- obviously, for the less-painful purchase price; and you're also going to be hard-pressed to find anyone who services them, should that ever become necessary, whether they be cheap or expensive models. A tech friend of minw, who is familiar with them, mentioned that both the electronics and transducers, in most of them, regardless of the price, are now absolute crap, and often supplied by the same vendor.
Years back, we had a couple of the pricier ones -- those that could seemingly rattle your teeth from a meter away -- and when we made inquiries about some valve repairs, were told that it wasn't even worth the effort -- "planned obsolescence," was mentioned; and that they would even have to be shipped, at considerable cost, out of state.
I currently have a VEVOR 6 Liter Digital Ultrasonic Cleaner -- about US 100.00 nowadays -- which has been heavily used for about five years, without missing a beat.
When it eventually craps out, it will simply become a tomato planter . . .