They go by the weight of animal. I had 2 puppies spayed recently (both in the 30ish pounds) and spent about 100 dollars each edit: forgot to mention shots.... Sorry don't remember the fees, they are fairly friendly there so give them a call, they can quote up front.
I don't know about shots but we got a grant from an organization called Friends of animals and I paid $40 to get my son's dog neutered.
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