I'm told there's an "thin client" class of computers. Ebay may have a few used variants that get close to your target cost, look for the HP t620 / t630 / t640 s

I'm told there's an "thin client" class of computers. Ebay may have a few used variants that get close to your target cost, look for the HP t620 / t630 / t640 series for examples but I am also getting hits searching for used enterprise network thin clients, with prices in the ~$45+ range. I'm considering something like this if at some point I decide to upgrade from my RPi 4, which is currently RAM limited. ServeTheHome did a one-liter PC series they called Project Tiny Mini Micro, that features small units that hit everything you ask for except cost (buying used might avert the ~$250-$800 price tags I see)