Even if a figure is 100% reused that doesn't mean design time is not involved. And very few of these figures are just complete repaints. And even if they are it would be normal that a die(mold) would need replaced or repaired. There's also assembly. (Look at how many pieces an IM figure has compared to say hawkeye, or thor, or batman)
Raw materials. License fees. Manpower. Shipping (can cost up to or over 100k to get one container shipped from China to usa, thru customs) Getting approvals. It takes a lot of time and money to make these. They have to meet individual market standards and be tested. Even adult collectibles.
Compare this to a line like motuc. 75-90% reuse of parts on most figures. Subscription only(more or less). Cost has gone from 20 each to 30each. Near zero articulation. Limited paint apps. Heck even the newer Giants (classic figures in 12 inch) cost nearly a hundred per figure for about as simple a figure as you can imagine, with almost complete reuse of tooling. For figure cost I've heard for each articulation joint it can add 10-20 dollars per figure. That was awhile back(ten years ago) so I'm sure the cost has dropped as better tech/manufacturing has emerged. But still, when a 12 inch motu figure cost nearly a hundred bucks you can see why hot toys cost what they do.
