I have a 1977 Peugeot UO-10 and will keep it forever.

Gee, that's hard to say about yours, I guess it depends on what shape all the components are in. You can replace the cables, seat, tires & wheelset cheaply. You can replace the derailleurs and leave them in friction mode, that won't cost much. If you replace the downtube shifters with modern index shifters, the cost could build pretty fast. I understand the b/b is from a older standard and hard to find.

My bike has a new seat, and straight handlebars, but otherwise is original. It works fine and is a nice ride.