Spray affected plants with a ready-to-use systemic insecticide that contains acephate, imidacloprid or dinotefuran. Systemic formulas do not kill bagworms directly. The active ingredient is absorbed into plant leaves and needles, and then circulated throughout the plant. The insects die when they feed on plant parts and plant sap.
Depending on the size of your garage, insulating the walls with batts of R-13 will typically run you about $400, the ceiling $600, and the garage door will cost about $600 if you do it right (See image to the left). You can use the pink Styrofoam stuff from Home Depot, but that will only insulate your door to about R-6.
The price of $45 per square foot ($60 per square foot if insulated) applies for a base model garage, non-insulated, built with standard materials. If you elect to use high quality materials, the price will increase to about $55 per square foot ($70 if insulated) for an non-insulated garage. It is important to note that the above-mentioned amounts only include the construction of the building itself, meaning material and labor, and are only approximate.