When my 135 lb bullmastiff was still alive, we visited Hilton Head and stayed in a hotel with him with no problems. I can't remember the name of the hotel, but I think it would be even eaiser to find one since you don't need an unrestricted weight limit.
It's peak season now, so dogs are only allowed on the beach early in the morning and later in the evenings. Here is the link to the rules (scroll to Animals on the Beach section):
Hilton Head Beach Ordinances | Shore Beach Patrol Lifeguards
ETA: Here's a good place to start for the hotels:
http://www.bringfido.com/lodging/cit..._island_sc_us/