servethehome.com has a series about these fanless, multi-gigabit firewall for a while, might be interesting if you have a 200-300 USD budget?

www.servethehome.com/tag/firewall/

I’ve used a very similar setup in the past (J1900 CPU, 4x1 Gbps network ports) and I only replaced it due to reasons. Not noticed any performance bottle necks with that setup.

The latest N100/N200/N300/N305 CPUs from Intel looks really interesting, similar performance as my workstation but at a 10th of the power usage. N305 also has 8 cores in a passively cooled case, amazing stuff!