LF: Inexpensive Canister Filter (EDM)
 

need cheap canister filter for vacuuming out my sump

May I ask, is the canister going to be below the water level in your sump? If not, I suspect you'll have a lot of trouble getting it running as they operate on a siphon basis rather than running a vacuum.
If you want to clean gunk out of your sump I'd buy a cheap wet/dry shop vac and drain as much of your sump as possible then hit it with the shop vac.