GP said "LPDDR5" and that Apple won't sell at component prices.
You mention DIMMs and component prices instead. This is unhelpful.
See https://www.digikey.com/en/products/filter/memory/memory/774... for LPDDR5 prices. You can get a price of $48/chip at a volume of 2000 chips. Assuming that Apple got a deal of $30-40-ish at a few orders of magnitude larger order is quite fair. Though it certainly would be nicer if Apple priced 8GB increments not much above $80-120.
I am aware that there are differences, I just took RAM DIMMs as a reference because there is a >0% chance that anyone reading this has actually ever bought a comparable product themselves.
As for prices, the prices you cited are not at all comparable. Apple is absolutely certainly buying directly from manufacturers without a middleman since we're talking about millions of units delivered each quarter. Based on those quantities, unit prices are guaranteed to be substantially lower than what DigiKey offers.
Based on what little public information I was able to find, spot market prices for LPDDR4 RAM seem to be somewhere in the 3 to 5$ range for 16GB modules. Let's be generous and put LPDDR5 at tripe the price with 15$ a 16GB module. Given the upgrade price for going from 8 to 16GB is 230 EUR Apple is surely making a huge profit on those upgrades alone by selling an essentially unusable base configuration for a supposed "Pro" product.
You mention DIMMs and component prices instead. This is unhelpful.
See https://www.digikey.com/en/products/filter/memory/memory/774... for LPDDR5 prices. You can get a price of $48/chip at a volume of 2000 chips. Assuming that Apple got a deal of $30-40-ish at a few orders of magnitude larger order is quite fair. Though it certainly would be nicer if Apple priced 8GB increments not much above $80-120.