Apparently a Pi running Pihole overheats. The Seeed mini (Pi CM4) is 150usd. https://www.seeedstudio.com/blog/2021/06/11/how-to-build-a-raspberry-pi-router-step-by-step-tutorial/
Being a computer guy, I guess I'm spoiled as I have 15 desktop computers, all of which can have 2 NICs and run pfSense. Even an old desktop computer from 2005 can be used as a router with decent performance: https://duckduckgo.com/?t=h_&q=build+a+router+out+of+an+old+pc&ia=web
Another choice is to check craigslist and compare the results with hardware and features supported by ddwrt/openwrt/tomato.