Used Intel 8th gen based mini PCs seem like a pretty good value. 100-150 bucks for a pc from a somewhat reputable brand (lenovo, dell, hp) with slightly better multi core than N150 and ~6W idle if you manage to get it to stay in C10. Some of them have a low profile pcie slot, like M720q and M920q. Also the CPU is socketed so you could technically upgrade it to e.g. i9-9900K, at least the M920q is known to take one as long as you use a powerful enough PSU. Few of them (at least M920q) also support coreboot due to an Intel Boot Guard vuln which could be fun, I'm planning to look into whether it could be ported to my M720q as well.
Update on power draw for anyone interested: measured with a cheap AC power meter, I get 2.8-4.2W idle with occasional jump to up to 8W on my M720q with i5-8400T, 16GB ram and a single nvme drive. This is on Debian 13 with ASPM enabled for everything and a few containers running (home assistant, esphome, bookstack, tailscale). According to powertop stats on C-states, it's mostly in package C9 and core C10.
