On average, listings lease in the $30's per square foot per year. The Charleston submarket is going through a decline in rates. In the last 3 months, the median rate fell $3 per sqft per year. That's a 8% decline in rent.
In the last 90 days, 72 listings have been listed, so you'll want to check back regularly for new listings. About 3% of the available leases 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 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 1,400 sqft. Most buildings in this area are approximately 2 floors. Most buildings in this market were built in 1985 and are Class A.