The typical asking rate per listing is in the $10's per square foot per year. The Mandan submarket is experiencing a decrease in rates. In the last 3 months, the median rate decreased $5 per sqft per year. That's a 26% decline in rent.
In the last 90 days, 1 listings have been made available, which means leases most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 100% of the available leases in the Mandan are subleases, so you might be able to sign a shorter term by taking over a previous lease. 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 area were built in 2003 and are Class A.