If you have an old PC with 2 ethernet ports laying around or you can get one cheap I suggest you build your own: https://arstechnica.com/gadgets/2016/04/the-ars-guide-to-building-a-linux-ro...
Yes any old PC combined with opensource OS is great "router". Some find the two OS groups below simpler to understand and run than "Linux" due to having less layers of abstraction, have less moving parts due to being developed in one house, run on same platforms... PC small FF, embedded boxes, non forceful freedom copyright, etc... used to run big tor relays too!
https://www.freebsd.org/ https://www.nomadbsd.org/ https://www.furybsd.org/ https://www.ghostbsd.org/
Have fun.