Still, "coming out ahead" isn't the reason for being for most of us on this forum. We just like the look and feel of old bikes. We hate to throw away things that are still "good". We like to prove that newer - or more expensive - isn't always better.
Case in point: I am currently building up a frame from what once was a chain store bike, which I bought as a parts donor in 2012 or so. Its brethren have ended up in landfills long before that. Yet, it is my size, its geometry is interesting and it's technically sound, so I kept it and now I'll build it.
The plan with these projects is always to keep it cheap and use what I've got. And, as always, I'll be offering up the nicest stuff from my bins, like a set of MAFAC "RAID" brakes, a Stronglight seatpost, a pair of Honjo fenders ... And, as always, I've already bought stuff especially for this build. A nice TA mini front rack is currently on its way from France, as is some leather bar tape from Poland ...
And, as always, I will have spent hundreds of dollars by the time this cheap build is finished. Coming out ahead? Not a chance.