The first XKCD was published closer to the release of the original Doom than to the present day.

That's not even close: the first XKCD was published closer to Intel's release of the 386SX than today.

18 years before XKCD, a 386-based PC capable of running Doom would have set you back $6,000–$10,000.

Imagine a game released today that has a 64-core CPU and a 4090 as minimum requirements, and that's roughly what Doom's system requirements would have looked like in 1987.

That was the entry price of legit Compaq Deskpro 386 on first release.

Within six months hobbyist computer enthusiasts were paying half that (or less, IIRC) for PC clones direct from asia.

Source: That's about what I paid for a Doom capable PC at the time.

A pair of second-generation T800 transputer chips and a 4-chip array board to fix them to cost way more at about the same time.