Fin Fang Foom wrote:
I would venture a completely off-the-top-of-my-head guess that, for the earliest volumes, it might have been somewhere between 500-750 copies -- though it's obviously much less now.

 500-750 copies--for the regular editions? And in their heydey, yet? Sorry, but I find that very hard to believe, FFF, since the painted-cover TPBs are the "common ones" and the variant ones the "limited editions." Back before I knew there were far-more-easier-to-find regular editions, I made the "mistake" of buying the first Spider-Man volume in variant form. On that back cover is a blurb that reads: "This edition is limited to 1422 copies." If the limited edition ran 1422 copies, then the regular edition had to have been more than that by the very definition of "limited" vs "regular". Maybe today the Golden, Atlas, and even Bronze Age volumes are printed at lesser quantities due to smaller or gradually waning interest, but the Silver Age regular editions have to be fairly high since these are the one most popular. And the earliest volumes of the series, which you were referring to in your off-the-top-of-your-head guess, definitely have to be higher.