1. Most will be able to learn to oil and grease vintage machines.
2. Not everyone is comfortable working on machines.
3. We who work on machines have not seen this one. Is it possible there is an issue you have missed?
4. Overhead varies a lot depending on location.
5. Level of overhaul varies among techs. It is not out of line to a) shop around for price and b) ask what will be done and c) is there a warranty on the work?
6. It is likely that tune-up on a 'modern' machine will cost that much, and also likely to need service again long before the vintage machine will.
I'm just saying, prices vary depending on a lot of factors. For an oil and lube, I think the price is high. For a machine that is glued together with bad oil, and requires a teardown, maybe not.