The typical asking rate per listing is in the $20's per square foot per year. The Greater Portland region is going through a an increase in rates. In the last 3 months, the median rate rose $2 per sqft per year. That's a 7% rise in rent.
In the last 90 days, 435 listings have been made available, so you'll want to check back regularly for new listings. About 6% of the available space in the Greater Portland are subleases, so you will probably have to focus your search on direct office leases. 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 1,840 sqft. Most properties in this region are around 2 floors. Most buildings in this area were built in 1985 and are Class A.