* 11 in 1 Panorama External Antenna (LG-IN2447) around $500. 4 internal cradlepoint antennas, see photo below. In retrospect would not have invested so heavily in wifi antennas and bought more 4g. I also added a little antenna lifter to make sure it has line of site of all cell towers, I wanted it to be the highest point on my sprinter van roof.
* Cradlepoint IBR1700 1200M-B around $900 on ebay. Runs on 12 volt, a ton of antenna ports has 1 internal modem that supports big US carriers, came with an additional modem that does the same for carrier aggregation. A bunch of different ways to configure the router to aggregate links, mostly I switch back and forth manually, I found that if there was an issue it would be obvious and I could just switch the link. Cradlepoint software wouldn't handle issues and signal strength that well. Honestly one carrier has been plenty good for me though and between ATT and Verizon, I only have issues in the national parks where there are cell dead zones.
* Verizon and ATT 4g cell plans. I added 1 line on my family plan for Verizon and the same with a friends family plan with ATT for $20 a month each. Took some phone calls into support to get it to work but after some escalations in the support chain I have unlimited 4g data. Total bill is around $50 a month.
* Still room to add more sim cards and more antennas. It honestly works great though, get 20-150 mbps basically everywhere.
Photo of my antenna and cradlepoint router/modem: https://imgur.com/a/MOdJkT8