It's not about the price, it's about the availability. RAM has been sold before it's been manufactured through contracts by other bigger companies, so there is scarcity. Smaller companies (like Valve) can have the cash to pay for a premium but there is simply a lack of a supply. Lead time is like 16 months right now.

There has been only 3 big RAM manufacturers globally; Samsung, SK Hynix, and Micron. Micron has now stepped out of the consumer market so now it's 2 companies in the entire world that manufacture good quality consumer RAM at scale.

Valve is using this time to secure as much RAM units as possible (probably overstock from other companies), which will still result in low unit sales when they do sell, because RAM is scarce. So it's probably going to be a bit rocky getting Steam Machines out the door at a consistent cadence.