I've been using my ZTE Mobley w/ AT&T data service with Echo Dot in the car for a couple of years now. It provides 22GB of 4G LTE data for about $20 a month (comes to about $23 after taxes/fees). They stopped offering this about a year ago. But I'm grandfathered into this plan. The cool thing is I can move the ZTE Mobley to any other car I own at any time. It is just a dongle that plugs into the OBD port of any car.
But now AT&T is offering the same plan for $15/month but only if your car has built in WiFi. Many newer cars have this already built in. You just need to sign up for the service.
Here's the link if you want to find out more:
https://www.att.com/plans/connected-car/gmc.html