But you can build something similar to a TBE very easily.
A 50 litre or bigger picnic cooler. Not that expensive new and many people have an old one kicking around. It'll be insulated,have a drain and a lid. All good things.
A 300 watt fish heater isn't much money either.
A little aquarium pump to move the water around is an added luxury.
If you need bigger just get a bigger cooler and heater. Or even two heaters.