The first DIY project I ever tried involved putting a brand-new, $250 Seagate 25MB HDD into my Xerox-brand 8086-based XT. (Yeah, yeah, yeah, so I'm old.) My wife and I did it together and felt so much satisfaction that, when 286's came out, we bought a big roomy case and built our own from scratch. We learned some things - like, I was better researching the components and finding parts in the bins at the San Jose Fry's store, but she had a better instinct for fitting it all together - where to run the wires, how the clip works on that memory stick, whether to apply some force or stop and take a closer look.
I don't think we've ever not had a system build in progress since then. I suppose we're just natural-born geeks or something. A long time ago, I stopped comparing the costs with what a prebuilt machine would cost. Somewhere along the way, that kinda stopped being the point.
One of those builds in particular still stands out in memory. It was in the late 1990s, putting together a machine for middle-of-the-road use with business apps. After I checked outputs on the used PSU I forgot to unplug it and when my wife hooked up the mobo all the magic smoke came out. The office stank of burning epoxy for weeks, but at the moment when the smoke started to rise my wife and I looked at each other, and started to laugh. I don't think we stopped laughing for at least ten minutes. I mean- we'd been waiting to see the magic smoke for more than 10 years, and when we finally did, the main thing we noticed was how awful the magic smelled.
Hey, bang for the buck, or making the box your own motorcycle-style, or winning your geek credentials, or whatever - that's all fine. We build our own because it's fun.