A full-scale apartment or guest house will take you to the top of your budget and beyond at an average between $15,000 to $30,000. You'll need to make all the upgrades mentioned for a family room, along with a separate bath and kitchen. You'll need to run a gas line or a 220 outlet for the stove. You'll also want a private entrance for your apartment, which usually entails adding a fire door.
Older homes have smaller garages. This is a simple architectural truth. In the past cars were smaller, and most families owned a single car. This means your older home has less garage to work with. Where a new home may have a garage that is up to 50% of the square footage of your home, an older home may have a one car garage that is no more than 200 square feet. Knowing how to remodel a small garage begins with knowing the 5 P’s.
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.