The typical asking rate per listing is in the $10's per square foot per year. The South Portland region is experiencing a an increase in rates. In the last 3 months, the median rate went up $3 per sqft per year. That's a 15% increase in rent.
In the last 90 days, 23 listings have been listed, which means spaces might be going fast. You'll want to be prepared to tour spaces as quick as possible. About 4% of the available leases in the South Portland are subleases, so you will probably need to sign a longer term lease with the landlord directly. 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 2,440 sqft. Most properties in this market are around 2 floors. Most buildings in this area were built in 1974 and are Class A.