On average, listings lease in the $20's per square foot per year. The Portland submarket is going through a a rise in rates. In the last 3 months, the median rate went up $1 per sqft per year. That's a 7% increase in rent.
In the last 90 days, 44 listings have been made available, so you'll want to check back regularly for new listings. About 2% of the available leases 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,830 sqft. Most buildings in this area are close to 3 floors. Most buildings in this area were built in 1900 and are Class B.