Cheap mesh repeaters... if you have a solar patio light that already charges a 18650 battery, then you can use the seeed studio xiao module for $23. https://a.co/d/04WBxe5e

Otherwise if you want to build something that needs a solar charge controller, get the RAK 4631 starter kit. https://a.co/d/03hLSa40 .

I tested several 900mhz "fold over" antennas yesterday and they had an SWR of 1.5:1 when straight and 1.2:1 when bend at 45 and 90 degrees.

I'm just a sucker for a "real" antenna. You can find fiberglass 5.8db 900mhz antennas for around $32-$35. They will be around 18inches long. Be aware you will need a short cable to adapt the IPEX connector on the mesh boards to an N connector.