I know a vet in my area that does it for $35. It really just depends on your vet! Also, if a vet does charge a ridiculously high amount it might indicate that he or she is not comfortable with doing the surgery. Though it is not uncommon for neutering to cost $80 or more, even with an experienced vet. It depends on the area you live in too.
I've heard of it being as low as $25 to $30 when multiple rats were being done & I've heard of it being as high as $200
I think $200 is high but I'm also old enough to know about the saying "you get what you pay for"
I found a web site that lists vets that specialize in exotics, it might help you narrow down your search & by all means, when you think you have found a vet that you will use post their name & see if you get any first hand feedback.