I remember in 2007, buying my first MacBook. It came with an enormous 2gb of RAM. I asked about upgrading it. The guy leaned in conspiratorially and told me that Apple’s RAM upgrades were a rip-off, and that I’d be better of buying it elsewhere. So I did, for half of what Apple were asking.
This is a grift that Apple have had for far too long, and there’s a part of me that’s convinced that their move to soldered RAM was to stop people upgrading after the fact more than it was about SOC efficiencies.
I do periodically look up their prices on eBay, but because of that weird aberration they’ve retained their value pretty well.