I hear ya, and I feel your pain
I do have to disagree with the comment about repairs, or as known CLA, clean, lube and adjust.
I purchased a GSN from a fella who worked f/Yashica until he retired, located to Atlanta GA, and started a business restoring Yashica cameras. He is the Yashica Master, and anything you get from this guy is as new, period, seals and all.
$165.00 US paid for this jewel, and I have bought three from him, I would not take less than $300.00 even if I were willing to sell. I have a manual f/a GTN set that has the following info wrote on the back of it, Yashica GTN kit complete $225.00, 1978, now if it cost that then and with today's inflation, to purchase this outfit now would be well in the $1000.00 range
. Why do you ask since I can go to eBay and bid until I win, pay and get f/$35.00. Here's the flip, fungus in lens, battery compartment looks like a melted hot mess, flip the film advance and hit the shutter release (POD not), no little click sound that means the shutter is not operating, let alone the focus/range finder glass is cracked. Get the idea, I should know, I bought and repaired enough of them!
I know also some on eBay think, classic, that only applies to cars. When you have bought enough of them, you learn to ask questions and go w/your gut reaction.
I have @ this time over 10 models of Yashica cameras, all work and are in pristine shape. I have all the bells and whistles that go with them, pristine shape as well.
I have a small fortune in them, but not as a investment, but for the purpose of use and the pure joy of owning these little marvels of mechanical photography made in Japan.
Yes, I said use as long as film is still being made, I will take photos with them, after all, that's what they were made too do.
So, in answer to your question, how much you spend depends on how bad you want and what shape the item is in.
Please do not get me wrong, I have purchased GSN 35's f/$25.00 that still took great photos, right up until sending for a CLA. A CLA will run you $150.00 today's price.