In my area spay/neuter clinics are bare bones - no pre op bloodwork, no pain medication afterwards, no removing retained baby teeth, etc. With the high incidence of liver disease in Yorkies, it is imperative they have pre op bloodwork since anesthesia is processed through the liver. It could save their life. If the spay/neuter clinic doesn't offer it, you will have to get it done at your vet's office beforehand. Make sure you add that to the cost of the spay quoted by the spay/neuter clinic.
It is very important that the vet use either isoflurane or sevoflurane gas for sedation. Keeping the dog warm, especially with sevo which can lower the body temperature, is also very important. One of our members recently lost her Yorkie because the proper anesthesia wasn't used. She also didn't have per op bloodwork done.
http://www.yorkietalk.com/forums/sic...-my-lexie.html
Yorkies tend to retain baby teeth. They are commonly removed during the spay or neuter so only one anesthesia is needed. It will end up being more expensive if you have to have a separate procedure done to remove baby teeth not to mention putting your Yorkie at added risk with a second anesthesia.
My local SPCA offers vouchers for a reduced cost spay or neuter than can be taken to your regular vet if he participates in the program and deducted from the overall cost. I personally would be much more comfortable with my own vet than a spay/neuter clinic.