What's the cheapest best dewormer?

We rescue cats (as well as dogs) and we've always just gone to the vet and gotten dewormer there but it's so expensive and we can't get it in bulk. What's the best & cheapest dewormer we can get in bulk that will treat roundworms & tapeworms (caused by fleas)? Thanks!

Generic Strongid (pyrantel pamoate) suspension is best for roundworms/hookworms/etc. It's usually sold for horses or humans.

For tapeworms, you can get Tradewinds Tapeworm Tabs. But they aren't cheap so it's usually cheaper to get Drontal from the vet :/. There are praziquantel fish meds that can be used but you need to make sure that there are no dangerous-to-cats additives and you need to be VERY sure to get the dosage right. Easier and safer to get it from the vet. Maybe if you ask your vet for a prescription you could order Drontal cheaper and in bulk from an online pet pharmacy.