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.
A pack of weather stripping material for garage door could cost somewhere between $10 and $20. Those with higher densities could cost a bit more, although the pricing can be warranted because of its increased durability.