Try not to notice Andrea's path, if storms will cross a place off your list!
I'd recommend Brookgreen Gardens for a visit. It is truly one of the top attractions in the whole state, filled with something for everyone. The statuary gardens are incredible, the animal areas are fascinating and peaceful, and the whole place is just a gem. One of my favorites. It will be a bit of a drive from Myrtle, but well worth the trip.
I think there must a ton of budget accommodations up there--big and small hotels seem to be everywhere. I guess it would depend if you wanted to stay on the beach or a few streets back as to prices.
If you want good food though, you are going to have to drive down to Charleston.