Buckminster Fuller wrote in one of his books that a geodesic sphere a couple miles in diameter, with solar heating making the interior air a couple degrees warmer than outside, would have enough buoyancy to float in the air, even with a whole town built inside it. (Though I think you’re right about “probably later!”)
As to the costs, after elementary amortization (over 10 years?) of the minimal capital outlay, plus negligible cost of fuel, and you’re pretty much left with staffing. Allocate a hundred thou per year for the part-time services of a supervising/maintaining engineer and techs, and divide by 5 megawatt-years, or about 40,000MWh, or 40,000,000 kwh, and you come up with 100,000/40,000,000 = $0.0025, = 0.25¢/kwh.
Once people have the option of setting up local power sources pretty much anywhere, lots of things are possible. Existing remote communities would likely be among first adopters, btw.
For a sci-fi book, how about stateless floating ocean communities? Also, check out “vertical farming”; it would integrate well into isolated urban clusters with independent power.