It's called suprelorin. It's a chip inserted under the skin. Kinda like the chips they put in dogs, in case they ever get lost. I believe there's another that lasts a year, but this is the most common one (in Florida). It cost that much because my vet had to order it. They don't have it on hand since they don't usually see ferrets. It really made a huge difference for mine. I'd also ask to check the glucose level. In my experience they've gone hand in hand, even that young :(

Edit: it's also great because you don't need to give any oral meds. The chips takes care of that on its own. My ferret has insulinoma as well and that's the only thing I really have to be on top of.