Most listings are in the $30's per square foot per year. The Mandan submarket is experiencing a a boost in rates. In the last 3 months, the median rate increased $32 per sqft per year.
In the last 90 days, 1 listings have been made available, which means listings most likley are going fast. You'll want to be prepared to tour spaces as quick as possible. About 900% of the listings in the Mandan are subleases, so you might be able to find a shorter term or below market rent. 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 2,000 sqft. Most buildings in this area were built in 1984 and are Class A.