Renting a car can be close to the same cost as flying, unless you find a fantastic price on air fare. A couple of years ago, I had to go to the Cleveland area, then to Williamsburg, VA, and then back to Chicago over the course of about a week. I rented a small SUV from Enterprise that got decent mileage and drove the whole way. Drove straight to Cleveland, then straight to Williamsburg. On the way back to Chicago, I pooched out just north of Indianapolis and found a cheap motel. This trip took about a week due to the timing of the meetings, and I think it was around 2,000 miles or so in total.
The reason I rented is that I didn't want to put the miles on my personal vehicle. Plus, I only charged my company for the actual rental fee and actual gas used, and didn't use our standard mileage reimbursement rate. This saved my company at least $500 or more.
I hate flying, as it is such a time waster. I never fly anywhere any more if the destination is within 500 miles. And, if I do fly, I fly out of either Rockford, IL (free parking, no tolls), or Milwaukee (cheap parking, and no tolls). I avoid O'Hare like the plague.