Most listings are in the $20's per square foot per year. The Charleston submarket is going through a a boost in rates. In the last 3 months, the median rate went up $7 per sqft per year. That's a 33% increase in rent.
In the last 90 days, 8 listings have come on the market, which means listings are probably going fast. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet on the market, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 810 sqft. Most properties in this market are close to 5 stories. Most buildings in this area were built in 1984 and are Class B.