The typical asking rate per listing is in the $30's per square foot per year. The Tualatin submarket is experiencing a a boost in rates. In the last 3 months, the median rate rose $32 per sqft per year.
Compared to the rest of the Greater Portland market, the Tualatin region has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 10 listings have come on the market, which means leases might be going fast. You'll want to be prepared to make an offer immediately. About 140% of the available leases in the Tualatin are subleases, so you might be able to sign a shorter term by taking over a previous 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 1,560 sqft. Most buildings in this area were built in 2001 and are Class A.