With So many places to buy exterior doors, it can be hard to find the best deal. Home Depot and Lowes both sell exterior doors. However, they both do not sell them at the cheapest price. I bought my exterior doors at Home depot, however, Lowes had a sale a week later, It was then I knew I could of saved a bit of money. You will want to measure the size of door you will need, It would take more time if you bought a door that did not fit the size you needed. If you need help, The staff at Lowes or Home Depot will help you.