Most listings are in the $30's per square foot per year. The Charleston region is going through a an increase in rates. In the last 3 months, the median rate rose $4 per sqft per year. That's a 12% increase in rent.
In the last 90 days, 129 listings have been posted online, so you'll want to check back regularly for new listings. About 5% of the available space in the Charleston are subleases, so you will probably have to focus your search on direct office leases. There aren't many listings below 2,000 square feet posted, 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 properties in this market are close to 2 stories. Most buildings in this market were built in 1986 and are Class A.