For me the vet bills are not the main thing, if a vet visit is needed, then so be it.
For me there are some other risks:
-You endanger the rest of your collection if you're not carefull by buying sick/mistreated/... animals. (One of the good reasons for isolation
)
-You'll be helping the persons selling sick/mistreated/... animals and they won't stop if people will keep on buying from them.
Most of the time there are other persons who do treat there animals good. So why take a risk?