Utilize small scale durable helium balloons. Very easy and affordable to scale up. Tie together a thousand feet, or more of 750lb parachord. Tether it to a large anchor of concrete, or bolt it down deep into the base of a large stump deep in the woods.

Put the meshtastic device inside of a small travel size waterproof pelican case to protect against the elements. Turn it on and let her fly.

You will need to check on your local laws and regulations to ensure that you are being compliant with air traffic laws. I don't think it should be a problem at that low of an altitude.

This should theoretically improve the line of site and bridge the gap gracefully. Possibly extending it even further. While requiring minimal weekly, or biweekly maintenance for reinflation.

If sourcing helium becomes an issue. Then you can make micro hot air balloons mcguyver style. Utilize the same methods to adapt to the change in deployment method. Then you are solid.

Let me know how everything works out. Hope I could help. Have a wonderful day!