There are 38 Diesel gas price reports in the past 5 days in Charleston, SC. The average Diesel gas price in Charleston, SC is $2.48, which is $0.32 lower than U.S. national average Diesel gas price $2.8.he lowest Diesel gas price is $1.86 of Sunoco located at 1628 Remount Rd, Charleston, SC 29406.The highest Diesel gas price is $9.9 of Exxon located at 5998 Rivers Ave, Charleston, SC 29406.he average Diesel gas price in Charleston, SC is $2.48, which is $0.32 lower than U.S. national average Diesel gas price $2.8.