The typical asking rate per listing is in the $10's per square foot per year. The Des Moines region is going through a a rise in rates. In the last 3 months, the median rate rose $16 per sqft per year.
Compared to the rest of the Seattle Metropolitan Area market, the Des Moines region has smaller rates, so you should have no trouble finding a great deal in this undervalued region.
In the last 90 days, 2 listings have come on the market, which means leases might be leasing quickly. You'll want to be prepared to make an offer immediately. About 150% of the available leases in the Des Moines 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,670 sqft. Most properties in this area are close to 2 stories. Most buildings in this market were built in 1984 and are Class B.