If you're patient and keep an eye on craigslist or kijiji you can get them fairly cheap. I've never bought a brand new canister filter, and I have six right now! Or if you have a local aquarium club... that's an even better way.
Well, if you're like me, my apartment complex said I can't have an aquarium over 10 gallons... So I have 6 of them.
mine is alright with the setups I have now, although IDK how much further I can push it, I'm on the second floor and will be moving in the next 1-3 years so thats a lot of tanks...but it's so tempting, I really want to get a shrimp tank going on my breakfast bar thing
I know I can fit a 20L up there but it would have to be an in tank filter to keep up with appearances