Okay yeah - now I remember. I was on a mesalamine rectal suspension enema for a while. That one must be generic. Probably not the same as your canasa, but very similar ingredient right? Maybe you could look into something like that. I was also on the cortifoam. Different stuff, but put in the same area.
Suppository is like a pill put up your butt, and enema is like a liquid? Is there any reason they want you to do the pill instead of a liquid? Seems like a pill might stay put better, but the liquid might cover/spread out better.
You might even ask the pharmacist to check similar items and prices with your insurance, they should be able to do that for you - then ask your doc.