We dove a couple of shallow wrecks a few years ago with
Express Watersports out of Murrell's Inlet - a few miles south of Myrtle Beach. Average vis in the summer but the wrecks were pretty small. And nothing nearby except sand. We dove the 11 Mile Tugboat/Plane wreck and the Bill Perry Wreck. The Perry is about 70', I think the Tugboat was closer to 40'. We might've done two dives per wreck due to the distances to anything else diveable nearby.
Express just bought a 46' Newton diveboat in 2007. They also do longer day trips out to the bigger, deeper wrecks out in the Gulfstream. Bathtub warm water near offshore, but you might want a skin as there were a lot of small jellies at one site.
Another option is
Coastal Scuba in North Myrtle Beach. Never dove with them but they seemed reasonable on the phone. We stayed in Litchfield Beach so Express was closer.