It isn't that simple. Destination has a TON to do with fare prices. Yeah - you save $220 by going from RDU to ICT instead of leaving from ILM. However if I were to fly Delta to SLC I save a grand total of $8 by driving 2 hours to RDU (Which will then be lost on gas and time). I fly at least once a month. I spend a great deal of time looking up flight information. In some cases it is absolutely cheaper to fly out of RDU (including the cost to drive there) but in just as many cases it is a nominal difference. With gas prices the way they are now it really needs to be $200+ cheaper to fly out of RDU to make it worthwhile and I'll be honest - out of 15 trips I have taken this year only 1 has been worth it to drive to RDU.