What kind of sensors do those cheap kits come with?
A tractor is a big thing to have rolling around unsupervised. I would want a lot of safeguards. Blindly going from one GPS point to another sounds like a nightmare.
Here you go, local grain farmer (4,500 hectares, barley, grains) reviews a fully automated driverless swarm bot in boom spray configuration:
The cheapie aliexpress specials simply drive the line they're programmed to drive. They have GPS and a gyro to account for the slope of the land. You're supposed to stay in the tractor while they're operating as a safety... but this doesn't always happen in some parts of the world.