My home router is a Lenovo ThinkCentre Tiny with a Core i3-8100T with a dual 10Gbit SFP in it (1x DAC, 1x 10GBase-T) and it idles at 14W, routing 10gbit full bore, 24W. I got it for $80

I also have some Fujitsu office machine I picked up for $50 as my "I need to run some random task on a physical linux box" machine with an i5-7500 and it idles at 15W