1 Depending on the size of your horse and the type of feed that you choose, the average horse will eat anywhere from $1.50 to $6 per day worth of food. 2  According to BackintheSaddleProject.com, weather slightly plays a role in the volume of feeding. 3  Horses are fed more in winter to keep them warm. If you buy it at the feed store, it will cost $2 more. 2  Basing it on pick up price, Alfalfa hay will come out $0.16 per pound multiplied by the weight of the horse, and its daily consumption will cost around $4.40 per day for hay.