The costs of neutering should include the general anesthesia as well. You may have to pay extra for the neutering procedure if the dog is in heat or obese. Most vets will charge a flat fee of $25 to $50. If the dog is pregnant, the spaying may cost more (an extra $50 to $100).After the surgery, the dog will require pain medication, which will cost something extra.he costs of neutering should include the general anesthesia as well. You may have to pay extra for the neutering procedure if the dog is in heat or obese. Most vets will charge a flat fee of $25 to $50. If the dog is pregnant, the spaying may cost more (an extra $50 to $100).