I run a Unifi USG-1 router/gateway now but before that I got a used AC1000 router from the thrift store for $5 and loaded OpenWRT on that. I eventually got an Aris modem to replace the Comcrap Gateway because it was messing with the DNS traffic, even when piHole was set as DNS for every machine. So if I were you I would go look at the OpenWRT list of units that will accept their firmware. Pay attention to the hardware revision as well as the model number, it matters.