You can give the game developer money, sign up for a service of some sort, or sign up to get spammed. One suggestion: if you want to get Farm Cash by signing up for the surveys and so on, skip the ones that want to text you something, and use an email address that is yours but not your main one. The spam gets sent there but your main account is safe.
You can raise crops and herds to get to a point where you can “buy” all the extra barns and stuff with the profits from your farming. Some people just don’t want to wait that long.