Point to point WiFi is low cost and works great as long as you have line of sight.

Exactly. And if you don’t have line of sight, you can raises masts and put them up higher. Tight beam patterns will go long distances.

Then on the same mast you can install a ‘wide’ powered emitter- basically a narrow beam formed that only covers the open area. You’ll still have ‘dead’ spots out there, but it’ll be a lot less.

Sticking with 2.4ghz will help a lot too- more bendy than 5.4ghz. Specialized gear can go lower but now you’re looking at insane prices.

So long as you have juice at each location you can have coverage, albeit with increased lag/hops, but it’s totally doable.

Check out the Pico UPS and other devices they sell. Looks like you’ve hit all the big parts out- I’d suggest adding some large accumulation caps on the output just to carry over sudden surges but otherwise- AWESOME!