Argo- Where I live, vets charge wildly different prices depending on location, popularity of the practice, etc. We actually take our dog to a vet in the neighboring town rather than the closest one.

I like sd's suggestion. Even if the humane society doesn't offer those kind of dental services to the public, they might be able to give suggestions for vets that charge more reasonable rates or are willing to lower charges for rescue animals.

Poor pup.