I have never encountered this, so I can't speak for the price of the vet work at all. Odds are, the price hasn't gone from $85 to 400 due to inflation since Linda had it done.
In any case, most vets care more about the animal than the money, and if they know you can't afford lump sum, they will allow payments. Many will require their expenses paid up front (medicines, etc), then payments for the rest. That way they know that at most they will lose their time.
Based on this, I'd say the same as Linda...find another vet. Just call and ask them what they charge to do the work, and maybe you can avoid another visit just to diagnose the problem.