The typical asking rate per listing is in the $10's per square foot per year. The Irmo region is going through a a rise in rates. In the last 3 months, the median rate rose $1 per sqft per year. That's a 8% increase in rent.
In the last 90 days, 5 listings have been made available, which means leases might be leasing quickly. You'll want to be prepared to tour spaces as quick as possible. 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 1,900 sqft. Most buildings in this area were built in 2007 and are Class B.