Hi-
How far are you from Boston? You could fly from Boston to Jacksonville for around $210 (with one stop) and renting a car and driving the 3 hours north to Hilton Head.
We live on Long Island and drove last year. Ran into serious car trouble and vowed never to drive there again. Well, we got a new car since our trip in July and now we are driving down again in 3 weeks!!! Its about 16 hours from the eastern end of Long Island. We will leave at 2 am on Friday, and drive until SAntee, SC, getting there about 3pm, then spend the night, get up early and get to HH before lunch. Its challenging to say the least with the 3 kids in the car!! But, we really can't wait!!!
Check around different cities nearby HH and see what you come up with for airfare.
It will be worth getting there, believe me, HH is truly a gem.