Liz Buchanan BVSc MRCVS
The other question is, where have the mites come from? Most guinea-pigs might carry one or two mites but if they flare up suddenly, particularly in one guinea-pig, it is often because their immunity might have taken a bit of a dive. It therefore may pay to have the guinea-pig checked over anyway. A surge in mites, for example, is a good time to have their teeth etc checked.
If a vet appointment is really not an option, the practice nurse may do parasite checks - but always ask how this works as far as charges are concerned in advance.