You can find a good deal on e-bay if you look around a bit. Aquaclears have a lifetime warranty, and unlike the aquatechs you can also get replacement parts (usually impellers or shafts after years of use) for them. If you want a cheaper hob
I have a used Whisper 4 that needs cartridges but runs like new, $30 shipped. For that matter, if you don't want to use the whisper media I can send along a block of poret foam cut to fit the filter for another $5. Just rinse the foam out in tank water when you do partial changes, much better than replacing the cartridges and tossing out your main biofilter with the old one.