ZTE Mobley -- not sure it's for sale anymore because Trump admin blocked sale of ZTE products in USA for national security reasons. They might be reversing that however. Check with AT&T and see if you can get it elsewhere - people on eBay and Amazon are selling them with grandfathered unlimited data plans.
ZTE Mobley - AT&T Premier Business Center
The $10 plan (1GB at LTE then unlimited at 2G or 3G speeds - sufficient even to download large 6GB maps updates that require WiFi) is ONLY available online and can be hard to find -- it's the vehicle plan. T Mobile has a similar device and sure others do as well - cheap because they presume you're not sitting in your car streaming data all the time. They didn't consider motor home users who use it as their hime internet device!