Cost: $50 to upwards of $1,000.
Even if your garage walls have been properly insulated, many home builders do not bother with the added expense of purchasing an insulated garage door. This negates much of the purpose to insulation in the walls, since a thin sheet of aluminum does one thing best, and that is transfer both the heat and cold from the outside, directly to the inside. You can purchase a new insulated door for several hundred dollars, or buy an insulation kit for a fraction of the cost. These kits use thin sheets of double-bubble radiant insulation which is applied to the inside of the garage door where it will radiate heat away from the door in the summer, and hold heat in during the winter. You can also use foam board insulation for this same purpose.