My carrier is Google Fi — one perk is that they will give you free data-only sims (up to 10 I think?) and you just pay for the data you use like any other data. I have used old Android phones in USB tether mode this way, and it works just fine. So, rpi+old/cheap phone should do the trick.
One fun bonus is that if you tether over USB it will work as a WiFi dongle, too — the failover from WiFi to cell should happen on the phone, transparently iirc. Not sure if that affects you.
Caveat is that I did this a while ago, and their pricing structure may have changed. Finished to be a great deal but has slowly become another carrier with not much to differentiate it…
My carrier is Google Fi — one perk is that they will give you free data-only sims (up to 10 I think?) and you just pay for the data you use like any other data. I have used old Android phones in USB tether mode this way, and it works just fine. So, rpi+old/cheap phone should do the trick.
One fun bonus is that if you tether over USB it will work as a WiFi dongle, too — the failover from WiFi to cell should happen on the phone, transparently iirc. Not sure if that affects you.
Caveat is that I did this a while ago, and their pricing structure may have changed. Finished to be a great deal but has slowly become another carrier with not much to differentiate it…