At the last place I worked (3200 physical locations) we scrapped physical bypass ports/NICs because they seemed to create more site outage time than they ever solved (maybe there is actually a model that is reliable at scale, but we didn't find it).

A port physical state watch script tends to be better. I don't know what lower end gear has it though, some may even support that as a mode of their "WAN monitoring" instead of actively sending probes. Worst case I know Ubiquiti Edgerouters let you run your own scripts on the Linux base and it'd be a matter of running "primary port up ? remove vlan from backup port and add vlan to primary port : remove vlan from primary port and add vlan to backup port" in a loop every second (there may even be a native feature for it though so check that first).

Plenty used on ebay at low cost. Quad port 1G (two sets of bypass) go for $25. Dual port (one set) 10g-baseT is maybe $30ish. Fiber bypass nics are also available, they'll have direct fiber connectors rather than SFP+ though (bypass will be optical).