The oral & topical methods of Ivermectin are supposed to have less issues associated with them than the injected form. Still, if it were me, I would contact the vet & ask to give topical Revolution for the next couple doses. If it was the very beginning of an infestation, the one dose might take care of it, but you don't want them to get more of a foothold. So it'd still be a good idea to treat at least one more time, if not two.
And while it varies by the area, $100 for a visit that includes wound care & medication is pretty average. Visits that include tests such as fecals, skin/mucous cultures, x-rays, ultrasounds, blood tests, etc. will get even more expensive. Surgeries are often anywhere between $200-1000, depending on what's needed. I had a hedgehog who needed an ultrasound, surgery, and biopsy to diagnose hepatic lipidosis (fatty liver disease) & all of that cost well over $1000, plus the rest of the exam & medication costs.
If you're worried about vet costs, it'd be a very good idea to start considering your options now. Hedgehogs are pretty notorious for racking up vet bills & because of how quickly they can get worse, waiting for the next paycheck in a week or two weeks is not an option. An emergency fund of at least $500 is often recommended. And I would suggest looking into CareCredit (a credit card with no-interest payment plans available for amounts of $200+ in a single visit) and vet insurance. Nationwide offers an exotic plan & is the only one I know of in the US so far. It's only about $8/month for hedgehogs & while it's not as much coverage as their full plan for dogs/cats, it's still better than nothing, in my opinion.
~*~*~ Kelsey ~*~*~
RIP my sweet Lily ~ 6/12/08 - 1/20/12