Garage floor coatings fail for a number of reasons. First, the floor is usually not clean enough to receive a coating. Years of grime have to be removed using solvents and proprietary cleaners. These are sold at paint stores, hardware stores, home centers and industrial supply houses. If the floor is really filthy, consider pressure washing. Rent a machine that produces at least 1,200 to 2,000 psi. Also, buy some grease-cutting detergent at the rental store. Along similar lines, you might consider a steam cleaner if a pressure washer is unavailable.
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.