The Family Search Pilot Site has them for free from 1915-1943, they only indexed 1944-1955.

Ancestry.com has Charleston County Death Certificates from 1821-1955, South Carolina didn't make it law until 1915 for all counties to have a DC, so just about all started in 1915. Ancestry doesn't have all certificates for the 1950s up until 1955, some are indexes and some HAVE been indexed by Ancestry.