We use MikroTik for this. All manner of interfaces including LTE and 5G are available. I hear you can connect USB serial to them directly, but we also drop a surplus Dell OptiPlex at each location and attach the serial ports to that device. Total cost is <200 USD per site since we already have the older desktops laying around.
-- Hunter Fuller (they) Lead Router Jockey VBH M-1C +1 256 824 5331 Office of Information Technology The University of Alabama in Huntsville Network Engineering
