You certainly don't need lidar to do auto-steering on a farm that you own yourself. You can get decent straight-line results using a PID controller on a compass

You certainly don't need lidar to do auto-steering on a farm that you own yourself. You can get decent straight-line results using a PID controller on a compass alone, and tossing in a GPS module would make the whole thing even more accurate and robust. As as the OP said, there's already a bunch of open-source stuff out there to help make that happen.