A small storage unit (5 x 5, 5 x 10, 5 x 15) price averages between $30.00 to $110.00 per month. A medium storage unit (10 x 10, 10 x 15) price averages between $120.00 to $195.00 per month and a large storage unit price (10 X 20, 10 x 25, 10 x 30 ) averages between $200.00 to $325.00 per month. Compare storage facilities to get the best price.