> AT&T enterprise unlimited cellular internet, which the sim card can be had on ebay

Depending on your exact location relative to network towers that might work fine. I'm in Southern Vermont (Readboro) and had success buying $50 SIM cards from here: https://www.ebay.com/itm/4G-LTE-ATT-Unlimited-HOTSPOT-Data-5....

I eventually ended up going with VTel Wireless instead: https://www.vtelwireless.com. Speeds were about the same, it was a bit cheaper, and felt better to use a local company. I needed a good MIMO antenna to get good speeds with either. Good luck!