We got a home with a garage converted to a bonus room. The attic space is insulated though not enough, the AC is about 2 years old (3Tons I believe, have to make sure) and had the AC people add a vent to the bonus room. The bonus room has South and West (Arizona) exposure making it really warm in the summer. The rest of the house is cool, but this room is probably about 5-10 degrees warmer than the rest of the house. The room is probably a good 15 or more feet from the one return vent that I know off. Will it be beneficial to have a return suck all that warm air back to the cooling system? I understand that the cost of adding a return vent depends on many factors but could you give me at least a ballpark figure as to what I would expect to spend on it. Again, the room is about 15 feet from the main return vent and the attic is accessible.