On average, listings lease in the $20's per square foot per year. The Myrtle Beach region is going through a a rise in rates. In the last 3 months, the median rate increased $5 per sqft per year. That's a 31% increase in rent.
In the last 90 days, 8 listings have been listed, which means new availabilities are probably going fast. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,750 sqft. Most buildings in this area are approximately 2 stories. Most buildings in this area were built in 1996 and are Class A.