You can check out Pawleys Island, which is a pretty stretch of the Atlantic. It is not commercialized like MB. However, most of the rentals are for a full week. I would check out the
Litchfield Inn (beachfront) and
Litchfield By The Sea which is a condo community that rents out apts. There is also a Hampton Inn & Holiday Inn Express within a few minutes of the beach.
For real romantic visit but not cheap is the
Seaview Inn on Pawleys. A real nice B & B right on the oceanfront with all meals included.
The good thing about Pawleys is if the weather is nasty you can be in Charleston in about an hour, MB in 30 minutes or go down to Georgetown and walk around.