Leaky doors and windows let in uncomfortable drafts and increase heating and cooling costs. Check your garage service door to be sure it has good weather stripping and a threshold that seals tightly to the bottom of the door. In most cases, if your service door is missing a threshold and weather stripping, it’s more efficient to replace the door with a new, weather-tight version. You can buy an inexpensive prehung metal exterior door at home centers and lumberyards.
Like wood stains, masonry stains are less viscous than paints. They soak into the masonry and don't form a film the way paint does. Unlike film-forming coatings, stains won't make your garage floor feel like the deck of an aircraft carrier. Because of this, stains are somewhat more forgiving and easier to apply and reapply as they wear off and become dirty. One of the oldest (perhaps the oldest) masonry stains available is H&C, now owned by Sherwin-Williams and sold at local paint stores. This venerable brand has been used in the Southern U.S. for many years. It's available in a wide range of colors and it can be tinted to any color you prefer. It's available in two formulations: a solvent-base (that is unavailable in California) and a waterborne acrylic available nationwide. The solvent-based formulation is the tougher one, so if you have both available, choose the stronger route unless you're very sensitive to solvent fumes.
A garage remodel is usually much cheaper than a home renovation because the foundation, roof, and walls are already built. Many garages also have electrical and plumbing installed to some extent. The actual cost of a garage remodeling project, however, depends on what the renovated space will be used for. While a new home gym won't require much in the way of amenities, converting a garage to an office, apartment, or bedroom requires adding significantly more creature comforts.