On average, listings lease in the $10's per square foot per year. The Irmo region is experiencing a an increase in rates. In the last 3 months, the median rate increased $1 per sqft per year. That's a 8% increase in rent.
In the last 90 days, 3 listings have been made available, which means new availabilities most likley are 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 1,900 sqft. Most buildings in this area were built in 2007 and are Class B.