Most listings are in the $30's per square foot per year. The Charleston region is going through a a boost in rates. In the last 3 months, the median rate rose $5 per sqft per year. That's a 15% increase in rent.
In the last 90 days, 133 listings have been listed, so you'll want to check back regularly for new listings. About 5% of the listings in the Charleston are subleases, so you will probably have to consider a longer term lease. 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 2,000 sqft. Most buildings in this market are close to 2 floors. Most buildings in this area were built in 1986 and are Class A.