Great game! Add upgrades, more enemy variants, and difficulty levels, and then you could put a price tag on it. A few fixes that would be helpful: the time between nights – on my first try, I didn't manage to plant anything and lost (I don't think limited time is necessary when you're already limited by money and field size). Also, 1-day plants don't need to be watered (it would be better if plants started with 0 water).