Are you looking for just a place to stay, or something to do when you get here?
As you know, it is a long trip from SF to PDX. I am assuming that this means you may simply be looking for a place to sleep.
You could stop south of Portland at the Crown Plaza (I-5 at Hwy 217.) If you wanted to drive a bit further, you could go as far at Jantzen Beach (right across from the Washington boarder) and stay the Red Lion.
I would not waste money staying downtown or in The Pearl, if you simply want a place to sleep and then move on the next morning.