It depends upon your definitions of "good" and "router". If you are ok with <300 Mbps speeds, the Raspberry Pi 3B+ makes a surprisingly good router with openwrt

It depends upon your definitions of "good" and "router". If you are ok with <300 Mbps speeds, the Raspberry Pi 3B+ makes a surprisingly good router with openwrt. I suspect a lot of similar devices also work at Gbps speeds for very reasonable prices. If you also need an access point, the cost does start to increase a little, but it still isn't bad at all, IMO.