The most I ever paid for a sort of vintage bike was $40 for an excellent condition 1984 Fuji Club about 12 years ago that only had 5 miles on the bike! I eventually had to take off the Suntour ARX derailleurs, the rear derailleur never worked that great, I tried adjusting it, eventually took it to a shop, they adjusted and said it was working fine, but that the ARX series was never one of Suntour's shining moments. So, I took it off and put brand new Suntour Superbe Tech rear and Superbe Pro front I had in storage since the late 80's but never used. Now the bike shifts like a dream.
I did find a bike leaning against a dumpster, I spent about $120 on parts to restore it, not sure if that if that applies to your question.