Attaching single Etherent port device to two switches for resiliency

Hi,
I have an environment where I have a bunch of devices such as Avtec Outpost appliances that have a single Ethernet port and have no provision to install a second port or a replacement network card. I also have some point to point wireless links with the same problem - a single Ethernet port - resulting in the wireless backup link going away when a switch reboots or fails.

I want to attach the devices to an Ethernet switch, and have the connection failover to a *second* Ethernet switch if the primary unit is offline. For example, I need connectivity when the primary switch reboots during a firmware upgrade. So I am not looking at a switch "stack", or at some flavour of LACP. I am looking to have the device to connect to independent switch 2 if switch 1 goes offline and then resume the connection to switch 1 when switch 1 is back online. (Or it can stay that way until Switch 2 goes offline, no difference really)

I found the Omnitron iConverter GM3 which is a "Carrier Class Network Interface Device (NID)" that appears that will do the job, but it does about 20 things I have no interest in and is quite expensive per port.

Does anyone have a suggestion on a device that can do this? Preferably something that is rack-mountable and not hugely expensive.

Thanks