Caulk the Connection Between the Walls and Concrete Floor
Cost: $5 for a few tubes of caulking.
Many garages are not built using the proper compressible foam between the lower framing and concrete floor. What happens is over time this connection swells, shrinks, and moves, leaving spaces which will allow air from the outside to leak in. You can either use a foam sealant or a latex/silicone based caulk to seal this often overlooked area.