Most listings are in the $20's per square foot per year. The Mandan region is experiencing a a rise in rates. In the last 3 months, the median rate increased $1 per sqft per year. That's a 6% increase in rent.
In the last 90 days, 3 listings have been made available, which means new availabilities most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 33% of the listings in the Mandan are subleases, so you might be able to snag a great spot on a short term. 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 1,200 sqft. Most buildings in this region were built in 2003 and are Class A.