I have a "vintage" Pinnock made in South Australia in the 1950's and a very basic model Singer which I purchased new for $120 about 20 years ago. Never have either of these machines been serviced by a sewing machine technician....my husband regularly does a service and clean up, sorts out tension issues etc.
I know machines should be serviced annually. But mine tick over nicely with the "home" service technique.
If however, I possessed a new, computerised and less simplistic machine I would be inclined to seek professional advice and services. It's like cars really, old technology is easier to fix on the homefront. Once the technology gets complicated and units are sealed and computerised, it's time to use the experts. Also warranties can be void if machines are tampered with or serviced by people other than on the recommended repairers list.
You can save considerably by "shopping around" and asking for quotes. I guess though that is not always possible if you live in a more remote area. Maybe putting a little aside each week would lessen the "pain" of your workhorse's annual check up.
If you think about it, the cost of some of the newer machines is actually more than some of the cars we drive!