First it's your father-in-law looking to lease land, and now you are renting it...
Why would you think there is a "going price"? It's going to vary depending on where you live, like any other commodity. What I pay for gas isn't what someone on the other side of the country pays.
You can grow up to 6 plants in Weed, California. I'm pretty sure you don't need an acre for that.