If you don't trust your vet's decision, I would go and get a second opinion from another one. (especially if it will save you $35/dog). Vets make mistakes, too; they're only human. Also, make sure you are exactly following the directions on the bottle. If you are told by another vet to switch to the expensive ear drops, I would suggest getting the prescription from him/her and then mail-ordering from a reputable pet pharmacy (i.e. 1800PetMeds or petshed.com, which I have seen mentioned on PT before). This can save you some money on the meds and on refills, etc. I mailorder my Frontline Plus and Interceptor and am happy with the prices I get in comparison to the prices at the vet's office.

Good luck with the mites!