Cheapest Way To Get From Det. Michigan to Myrtle Beach SC??

For 3 adults (flying is out of the question...) what would be the cheapest way to travel from Det Mi to Myrtle Beach SC??? Train, bus, driving?? We are planning to stay only a few days....but any good websites with cheap fares for anything...rental cars, train tickets ect?? What do you think would save the most money????