http://www.dnr.sc.gov/news/saltpiers.html
that tells of a couple of the public piers both in Charleston and Myrtle Beach area, Bushy Park in Goose Creek is probably about as far inland as you will find saltwater/brackish water but I have never fished/crabbed there....I would personally wait till the water temp rises a little and hit the piers, fishing starts to pick up and the crab numbers will be higher...i'm sure their are more places to tryout but as far as the closest one with the best luck it's tough to say....hope that helped a little