Your estimates are not even close. You can't honestly think that LPDDR5 at leading edge speeds is only $3 per 64 Gb (aka 8GB), right?
Your estimate is off my an order of magnitude. The memory Apple is using is closer to $40 for that increment, not $3.
And yes, they include a markup, because nobody is integrating hardware parts and selling them at cost. But if you think the fastest LPDDR5 around only costs $3 for 8GB, that's completely out of touch with reality.
You can get 8GB of good quality DDR5 DIMMs for 40$, there is no way in hell that Apple is paying anywhere near that.
Going from 8 to 16GBs is probably somewhere between 3-8$ purely in material costs for Apple, not taking into account any other costs associated
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 $80-120.
As for prices, the prices you cited are not at all comparable. Apple is absolutely certainly buying directly from manufacturers without a middleman since we're talking about millions of units delivered each quarter. Based on those quantities, unit prices are guaranteed to be substantially lower than what DigiKey offers.
Based on what little public information I was able to find, spot market prices for LPDDR4 RAM seem to be somewhere in the 3 to 5$ 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.
A DIMM is 8 or 16 chips (9/18 is ECC), while the LPDDR is a single chip for the same storage. The wild density difference in chip capacity (512MB or 1GB vs 8GB) makes a huge difference, and how a stick can be sold at retail for cheaper than the bare LPDDR chip in volume.
This just seems like lameness on Apple’s part.