Starting cost is around 15m to the player you buy it from, then 5m for the barn itself. I’ll assume you’re growing potatoes. You buy seeds, fertiliser, and water every so often from the farmer’s market north of Kavala, costs about 15% of what you get. You almost always get 700 potatoes every half an hour, worth £1000 each, that can be sold at any market or gas station and take up 1 storage each. You make usually 1.4m/hour if you babysit it which is good moola