If the frequencies used are above the plasma frequency of the ionosphere (typically >30 MHz) like here then the only solution to "mesh" or cell networks is line of sight and that only comes from height above terrain. And height above terrain, except in rare and unique cases, is always expensive.

The only reason cell networks work is that the telcos pay big money for getting access, power, and backhaul to places up high. No amount of power increases, modulation gain, reflector aperture, software, or anything else you can think up is going to get around the lack of line of sight.

Unless a decentralized mesh network has enough money to do this it will only ever work in specific regions where single individuals or groups can pay $$$ and cover large areas. Like in Seattle where the mountainous coastal terrain is useful for hamwan's network, or in mega-cities like New York where residents have skyscraper roof access for p2p wireless community ISPs.