On average, listings lease in the $20's per square foot per year. The Portland submarket is going through a decline in rates. In the last 3 months, the median rate fell $2 per sqft per year. That's a 8% decline in rent.
In the last 90 days, 43 listings have been posted online, so you'll want to check back regularly for new listings. About 12% of the listings in the Portland are subleases, so you might be able to find a shorter term or below market rent. 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 1,500 sqft. Most properties in this area are close to 3 stories. Most buildings in this area were built in 1900 and are Class B.