I think the financial rules would be a problem if you did any more than a couple test transactions on #hamradio bands. Lowest frequency unlicensed I know of would be LoRa. I don't think there is enough adoption of node running to mesh up at those freqs though. #BlockstreamSatellite was my interest for a similar idea.
Discussion
I think it would have to be on the ISM bands, if it was in the ham bands I see the FCC cracking down on the nodes continuously broadcasting. Not trying to get anyone to lose their license.
The next issue I saw was an uplink either to a satellite or a few nodes sprinkled in that still had internet access to keep up to date with the rest of the network.
Nodes acting as repeaters to bring access to the remote regions is the best use case I can see right now