You could try one of the no-name canisters on ebay. I just bought a Jebao one rated for 350gph. Its basically an eheim 2080 knockoff, or something like that. I think it could easily filter a 140g tub by itself, and its only $89.99, with free shipping.
I've had mine for a month, and I like it so far. its the quietest filter in the house, is large (9"x9"x14") so plenty of media, and has a good flow rate. Its also very easy to set up, and super easy to prime. When I unplugged it from one tank to move it to another, I didn't let the water drain out of the hoses, so when I plugged it back in, it didn't need to be primed, it just started right up again.