I thought the total alternator rebuild would be the bearings, the brushes, the regulator, and the rectifier.
I can do worse than that. Of the two bearings I may only replace the front if the rear looks good and is too hard to get. The rear bearing usually lasts longer than the alternator because it has no belt load. That's why GM uses a big bearing in the front and can get away with a tiny cup of needle bearings in the rear. Many companies use smaller or lower quality bearings in the rear.
The brushes I just estimate the percent left and compare it to how long I think I'll keep the car. The cheaper they are the more I am willing to discard. Replacing early prevents damage to the brush commutators.
Bearings and brushes wear out all the time which keeps them cheap. The other parts including the regulator and rectifiers only fail catastrophically. Most never wear out which makes replacements expensive. I get them from a junk yard alternator or just let the rebuilders deal with it.
You might rebuild the whole thing for the education but it would cost more than a rebuild which is part of why those kits aren't around any more. When you learn what fails and what doesn't you can slash costs to a fraction of the rebuild price and have the same failure rate as a rebuild. A recent alternator rebuild on a 1998 GM full size was $10 for two bearings and $10 for the brush assembly. This regulator variant never burns out. That's $20 for another 150,000 miles. It was so cheap that I did the 1997 GM full size even though the brushes had some 40% life left. Getting my last $4 from the brushes just isn't worth it.
On my 1994 GM small car I destroyed a 3 year old C series alternator case front on a botched reinstall. The C rears are interchangeable and I have plenty but I had no matching fronts. After giving myself a swift kick for flubbing the Quad 4 Chinese puzzle bracket I assembled something resembling an alternator from the worst available parts and marched right down to Autozone and handed over the cash.