800mm^2 die would roughly cost 300-350 usd axcoeding to [1]. That's the Taiwan price and dor N4. This doesn't include the memory or the package. The silicon cost for N3 is close to 2x.
Well, seems that increase of 20% for US-based manufacturing on a base cost of $350 is $70. MSRP of 5090 is $1,999. So, on shoring will result in 3.5% increase in MSRP, which is nothing.