From another perspective, you could buy a cheap, rattly, tinny, riveted 7206 band from Rolex in the early 70s for under $50. Today that band would sell for $1,000 without blinking an eye. Maybe 3x that. Is that profiteering? No, it's supply and demand.
If you know your stuff, the frankenfield is a great playground. Pay what you know the pieces and watches are worth. If something is overpriced, watch it a couple weeks... I bet the price will come down.
If you don't know your stuff, then frankens are not for you. Go with stock from our trusted dealers.
A good corollary is buying a heavily modified Cobra kit car vs. a GT Mustang off the showroom. If you're good with wrenches, or can afford someone who is, buy the Cobra. Otherwise get the Muskrat and have 90% of the fun with almost no risk and instant gratification.