Yes, welcome to APUG. Good to have you here.
I might gently disagree with 'frank' on this one. If one were to make repair decisions based solely on the thrift store value of old cameras, none of us would ever be able to justify a single repair. And eventually none of us would have working cameras.
My own sense is that the calculation needs to be based not on whether the cost of repair exceeds the camera's eBay value, but rather that the cost is going to buy you a nicely working camera to enjoy for years and years to come. It's that future of enjoyment, and peace of mind, that you are really spending the money to secure.
Certainly you could roll the dice by repeatedly purchasing additional old ones until you eventually found one in decent shape. But that approach could likely exceed the cost of refurbishing the one you already own pretty quickly. And then what happens if
that one breaks? Then you're right back where you started, but after having already spent the repair money beforehand.
As for doing it yourself, I'd also strongly urge caution as well. Unless you have in-depth prior experience disassembling and reassembling high-precision mechanical and electrical instrumentswhich is exactly what a film camera isit would be best not to begin gaining that experience on a camera you are hoping to use afterward.
Here's an example. I purchased a used Canonet QL17 GIII 35mm rangefinder for about $90 after shipping. I sent it off to a well-respected technician for a $150 CLA. Here's a work-in-progress picture he sent me of the (only partially!) disassembled camera on his workbench...
Now I'm not saying that cleaning a viewfinder will involve this level of disassembly. The point is that, as mentioned by previous posters, taking an older mechanical camera apart is almost always more complex than it appears from the outside. Often special factory-created tools are necessary. And camera-specific knowledge is required in order
not to break other things out of ignorance.
So just some food for thought. For $240 I have a beautifully working and reliable instrument. Gambling on buying other used examples would have meant finding that needle in the haystack by the second try. The third try would have put me over $240 for a camera without a reliable CLA, and no more financial room to maneuver if that one then broke. And what if I didn't find the needle until the fourth try?
Best in the long run to just save up for the professional CLA.
Ken