Bear,
You have obviously priced them out and you are absolutely correct: if the ultrasonic cleaner was big enough to fit an entire MES rack, it would have probably cost several thousand. Fortunately, while mine was definitely a splurge (almost $300) it isn't in that league.
Mine is 9 liters (about 2 gallons) and I can fit one end of a 30" MES rack into it if I place the rack diagonally across the cleaner's opening. I suspend it by hanging it from my garage cabinet handle. I do one side (about 30-60 seconds is all it takes), and then flip the rack 180 degrees and do the other side.
Unfortunately, even after doing this, there are about 3-4 sections in the middle that still need to be cleaned by hand. However, since the tough part of cleaning the racks is where all the rack wires connect on each end (all those little corners...), the cleaner does most of the tough work.
I can also fit my mailbox mod (made from a popcorn tin) into the cleaner. This lets me get ALL the creosote off after each smoke, and makes it more efficient at condensing the creosote out of the smoke before that smoke gets sucked into the MES. I have to rotate the popcorn can in the cleaner because it too won't fit all at once. The smoke gunk comes off almost instantly, so the entire cleaning procedure for the mod is only 2-3 minutes.