Depending on income there are free spay/neuter programs. I'd call your local shelter for information. Otherwise it costs between $50 to $200.
Just keep in mind, you get what you pay for. Be sure a cheaper vet is reliable and competent. :)
Veterinary fees usually fluctuate depending on where the clinic or hospital is located. Hospitals in more affluent areas, or hospitals with large staffs and state-of-the-art diagnostic equipment charge a lot more for their services than the one-doctor small practices found in small towns.
The average price of an office visit is about $25, vaccinations run anywhere from about $10 to $20 per shot.
When it comes to spaying and neutering, spaying is the more expensive of the two because it involves actual abdominal surgery. It usually runs between $55 and $150 depending on the hospital, and also depending on the cat itself. It costs more to spay a pregnant cat because the blood vessels in and around the uterus are engorged with blood and there is an increased chance of the cat hemorrhaging, so more time and sometimes even a second doctor is needed, raising the price of the surgery. Pain meds following the surgery raises the cost about another $40, but for females I think it's entirely worth it, because I wouldn't want to have abdominal surgery without pain meds.
Neutering is considerably cheaper than spaying because it only involves a tiny little incision and no stitches, and the whole process only takes about 15 minutes, if that. The cost runs anywhere from $25 to $80, again, depending on the hospistal. My old vet only charged $21 for a neuter, while there's a big new hospital in town that charges $80 for the same surgery. Most of the time no pain meds are needed after a neuter, so that also keeps the cost of the surgery down.
Keep in mind that most vets will not operate on an animal that has not received its rabies vaccinations, so if your pets have not had them, add on the cost of rabies vaccinations.
As Savas said, wherever you go, make sure the vet is qualified. A low cost doesn't necessarily mean a lesser qualified vet, nor does a high cost mean that the vet is more qualified. Don't hesitate to first collect information from several vets and then take the time to ask around and check their qualifications before making your final decision. Make sure you choose the vet you feel most confident with, and not the vet with the cheapest price.
Better response then mine. :)
And neutering is cheaper than spaying because...it's a conspiracy!!! Against us males!!! We need to UNITE against the female scourge of emasculation!!! :)