Periodically, we do an informal survey of service centers around the country. Recently, I found a service center that charges a minimum of $325 for a standard service. In another region of the country I found a shop charging $65. One shop advertised $29.99, but upon a closer look their actual ticket price for a full service was over $90. There is some deception practiced by some shops, but most are pretty straight forward.
Generally, the more urban shops charge higher prices $200 to $300. Mid sized cities are charging between $100 and $200. More rural areas are commonly charging between $75 and $100. Some have explained they happily travel two hours one way just to have their machine serviced.
I encourage sewing machine users to find a trusted technician and support them accordingly. I encourage technicians to be fair to their customers and to themselves.