That's what it costs buying the parts from them.

$750 laptop, $360 RAM, $1000 SSD. The RAM is pretty reasonably priced, but you can get your own 4TB SSD for about $500 less. $150 less if you want the exact same model they're selling.

It's a much more reasonable level of markup than RAM/SSD upgrades from other manufacturers, though of course being able to bring your own is a major selling point.

Macbook with 64 GB RAM and 4 TB storage is $4600. I'd say that's pretty low.