Myrtle Beach would be my choice too. I cant wait for September to come. This year marks 9 years that we have gone to MB in September. I wish I had a place there but I dont. If it werent for grandkids here I'd be moving there after I retire, which is in 27 days
We stay at a place called The Dayton House, its kind of right in the middle of things at 25th and N. Ocean Blvd.. A short 3 minute drive to Broadway at the Beach. Without looking I dont know their summer rates, cause I go right after Labor Day, when prices plunge much lower. But with 2 teenage boys Sept. wouldn't work for you with school. Theres a ton of places to shop with 2 outlets centers. Very nice big Mall. Many places to eat, our favorite is Carolina Roadhouse.
Depending on how many stops on a trip down there, its anywhere from 6 1/2 to 7 1/2 hours on the road. I always come in from some backroads in North Carolina and come into North Myrtle Beach, not much traffic that way.