Check out the SenseCap solar node. It's way under $200 and professionally built.

https://www.seeedstudio.com/SenseCAP-Solar-Node-P1-Pro-for-Meshtastic-LoRa-p-6412.html

Probably the best configuration for it is as a regular client client_base role since that will relay like a repeater but without forcing other clients in the mesh to use it (which would be problematic unless you're in a super ideal position).

Edited b/c I forgot about client_base. See the reply to this one about that role.