An interesting dilemma. I have been finishing up a long simmering project over the last few days, and after running into yet another sticking point, briefly contemplated throwing in the grease rag. But I persevered and got out for the first test ride yesterday.
IYou mention money, parts availability, uniqueness of final product, and mental space as factors/issues in deciding whether to continue your current build project.
For me, money-wise, building up bikes is a self-supporting hobby. I mostly (except for the 3 brand new Rivs I acquired this year!) buy cheap old bikes that appeal to me in some way, and I maintain a kind of informal bike slush fund that is constantly replenished through selling bike related stuff. Even the Rivs were mainly funded this way, with an infusion from an old racing buddy who gave me a pile of old bikes and parts this past spring.
While lots of stuff is indeed hard to get right now, I do find ebay a good source for at least similar parts that will work in place of what might have been my first choice. And I agree with those that have said just get the bike rolling again with whatever, and see if it has the potential to earn a spot in your shed for a while.
Although I don't start out with "uniqueness" as a build goal, because projects generally start with a vintage frame with lots of beausage and get built up with an eclectic mix of old and new parts, they do end up unique in that sense--though not necessarily in function, which is another issue (and ultimately goes to the heart of the matter, but is ignored by those in the throes of bicycle building obsession.) It's definitely a form of expression--mostly to myself, and the occasional share on a google group or Instagram.
Ah, the mental space. For me, this takes up at least as much room as the actual bicycles and parts I live with. I'm determined to declutter both spaces in 2021.Having built up and ridden a lot of bicycles, I know it really is about Just Ride, so I won't have any FOMO. As much as I enjoy putting together a new build, the space virtually and physically is taking up too much room at this point in my life. My plan is to build up the remaining projects in the queue before my birthday in March (a Crust cargo fork bike, a BG Hikari, a 26" RTP go fast, and my 4th! Le Tour mixte build) and then start to figure out what goes. From there it will be tinkering with what I keep (and building bikes for my son, who is getting taller by the day.)
My latest, almost complete [black front wheel, bar tape, matching tires] a Sky Yaeger designed
SS Bianchi with Kogswell fork, one studded wheel.
Slight cross post from IBOB):