I would suspect in Southern California there should be some active selling of used aquarium equipment, I know here in Vancouver locally we have an active buy/sell area. I've bought a used aquarium from a Vancouver listing. Consider Eheim's or Rena's and look for used unit.
There are many varieties so first Google Eheim, then Rena to see what models would be suitable in your tank. Eheim have "classic" filters, these are the cheapest, I have an Eheim Ecco 2232 that works well in my 20 gallon tank. You might want to consider the next model up.
I'm not familiar with the Rena models but I know the filters are decent. But do check out the used market. Also its worth joining an aquarium club (Google or ask at your local retailer where on might be) as they have auctions very frequently. The club I belong to ($20/year) has auctions at every meeting, but two meetings a year, spring and fall, are reserved for the "big" stuff. At the last one you could have picked up aquariums, lighting, heaters, canister filters, plants, wood, substrate, fish, books, and a host of other goodies I can remember. Most items are almost given away. An Eheim 2217 was sold for $35.
Here's a link to begin your "canister education:" http://www.aquahobby.com/products/e_...er_filters.php