Minimum cost per day to keep one horse is $5.01 per day or $1828.65 per year. The costs quickly increase with: 1  feeding more expensive concentrates or supplements.2  you have unexpected veterinarian bills. 3  immunizing for other diseases such as West Nile Virus. 4  a horse that requires shoes.inimum cost per day to keep one horse is $5.01 per day or $1828.65 per year. The costs quickly increase with: 1  feeding more expensive concentrates or supplements.