I have an FM-2 that's been returned to Nikon on a couple of occasions for repairs. It's been a while since the last time, but my sense is that it's one of the models that they take pride in being able to support even though its a couple fo decades old - demonstrates their commitment to supporting tried and true Nikon photographers, blah, blah, blah.
If all that's wrong with it is that the screws have worked loose over time, the repair cost is likely to appear "high" - just because there is a fixed charge to take it appart and then reassemble it. If it were mine, I think I might combine that repair with a general CLA - on the basis that the total cost would be about the same. OTOH, if there's something more seriously wrong, the incremental cost of the CLA won't be all that high. In either case, at the end of the process I would have a camera that I would be reasonably confident would go for another decade or so.