I later added a large machine that I used to use as a Linux desktop, with a GPU and 64GB RAM, which I use for generating OpenStreetMap tiles.
I used to do this as well and this is fine if you're able to source cheap power. But I'm in the UK, electricity prices are insane and I can't afford to run this kind of setup any more.
a big ask in most of the UK, though.
Before RAM went crazy, the Pi 4 was $75 for *8GB and $125 for 16GB.
Another consideration is heat and power consumption, I have an OptiPlex micro (also surplus) and power consumption is 8W-90W (standby versus peak), 5x-10x more than a Pi 4.
I picked up 4, at £50 each, and when they arrived they were still sealed, and included a power supply, keyboard, mouse and windows 11 license (which never got used).
Makes the pi look like a terrible deal given you've also gotta buy power supply, a hdmi adapter for their moronic decision to use mini hdmi, etc