On average, listings lease in the $20's per square foot per year. The Tualatin submarket is experiencing a a rise in rates. In the last 3 months, the median rate went up $26 per sqft per year.
Compared to the rest of the Greater Portland market, the Tualatin region has smaller rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 10 listings have been made available, which means new listings most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 120% of the available space in the Tualatin 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 1,140 sqft. Most buildings in this area were built in 2001 and are Class A.