get a mikrotik they are good for the price and setup recursive routing
so what I'm using right now is 2 wans or you could use 1 wan and 1 4g or plug a phone on the usb port and turn on usb tethering
so basically recursive routing checks if a host is up on a line say isp 1 pings to see if 1.1.1.1 is up if not switch to isp 2
isp 1 is my own line and isp 2 is my apartment's shared internet connection that has unstable speeds but for failover,
it's better than nothing
get a mikrotik they are good for the price and setup recursive routing so what I'm using right now is 2 wans or you could use 1 wan and 1 4g or plug a phone on the usb port and turn on usb tethering so basically recursive routing checks if a host is up on a line say isp 1 pings to see if 1.1.1.1 is up if not switch to isp 2 isp 1 is my own line and isp 2 is my apartment's shared internet connection that has unstable speeds but for failover, it's better than nothing