What is the average cost of adding a bathroom in the same room where there is an existing laundry room?

Cost would depend on the size of the room, how expensive the cabinets would be, tub or shower, jacuzzi, etc... & if it's a do-it-yourself project. Depending on your "area" the price would be likely be more than double the price of your materials for labor. Do it yourself would save you quite a bit.