As it happens, I was reading about that very thing in an old Pop Mech magazine(ca. 1944) just a couple of days ago. So the idea has been around a while. (~80 yrs, m/l) And that just the printing of the idea.
For making one taper only, MT-1 or MT-2, for casual use, it would more than pay for itself the first time you re-centered the tailstock. Took me several hours the last time I did it on the big lathe. When I made one, it took less time than re-trueing the tailstock. Cost was... I don't remember, mostly stuff. I did buy the MT-2 mandrel, I was in a hurry at the time.
For more serious work, (repitative) I made a taper attachment a few years back for a Taiwanese nine inch machune. Used the idea from Gingery's book on building a lathe. The cross-slide portion........ It worked quite well at the time. I haven't built one for the Craftsman (12X36) because I haven't needed it. Yet.
I honestly don't recall how hard it was to set up. Too many strokes since. But it did the job at the time. Now that they're available on FleaBay, depending on the job load, they might be worth purchasing rather than building. Your call there.