How can i get to Knoxville TN from Chicago IL ORD airport, by bus?

I really need to know how to make this work because my flight is to Chicago ORD and my final destination is Knoxville TN. Google isn't helping much so I can really use someone's help resolving my concern. I'm on a Work and Travel program this summer and I've never been to the USA before. Another flight is out of the question and I have no idea what the train situation is. Changing buses is an option, and an estimated total of the cost of the trip in dollars would be of great help.