IIRC HUB did a recent video where they estimated a 5090 die costing $135, obviously there's a high chance of errors in such an estimate as things like TSMC wafer costs, defects vs good dies, whether Nvidia are getting discounts, etc, etc. All have to be accounted for so it's more a ballpark figure, however that's a lot more than $75.i bet you that in production cost, a 5090 costs $75 at most, R&D wont be much as Nvidia already have the infrastructure, their profit margins on GPU's are very high, even for a $2000 5090
That's just for the die. You then have to factor in the RAM, the PCB, SMD's, the cooler, packaging, etc, etc. If i had to guess the profit margin on a 5090 is probably in the 50-60% range and as you go down the stack that profit margin declines, it's probably why there's such a push to get people to buy only the highest end card.