Buy large cardboard boxes from HomeDepot.com and UHaul.com as of 2015. These websites offer boxes intended for both moving and storage and in various dimensions.
U-Haul offers cardboard moving and storage boxes in a range of sizes. The extra-large box available from U-Haul has dimensions 24-by-18-by-24 inches. A large box from the same company has dimensions 18-by-18-by-24 inches. These boxes may be purchased individually, though the company offers a discount to customers purchasing 10 or more boxes at a time.
The Home Depot offers large boxes with dimensions including 18-by-18-by-24 inches or 22-by-22-by-21 inches. The largest boxes available at The Home Depot cost around $2 each.