Most listings are in the $20's per square foot per year. The Portland submarket is experiencing a a rise in rates. In the last 3 months, the median rate rose $3 per sqft per year. That's a 13% rise in rent.
In the last 90 days, 40 listings have been posted online, which means spaces are probably going fast. You'll want to be prepared to make an offer immediately. About 3% of the office spaces in the Portland are subleases, so you will probably have to consider a longer term lease. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,500 sqft. Most buildings in this area are approximately 3 stories. Most buildings in this region were built in 1900 and are Class Class B.