In my opinion, and maybe it's just because I'm a bit of an Oregon homer in general, it doesn't really feel that much smaller. The only thing that felt noticeably smaller for me was the job market, and maybe if you wanted to go to NFL and baseball games (the basketball and soccer games especially are seriously great in PDX though). Unfortunately the traffic doesn't feel smaller than Seattle
The rent question... I'd still have to recommend a roomate I think. There's definately better odds of you finding a place in PDX than Seattle for that price, but still. In another thread, which I unfortunately can't find at the moment, a user was talking about how a lot of really old places near the city center were being renovated and put up for costs within that budget. Still though, Portland's got some serious rent problems too and I wouldn't want to give you false hope. You could do it if you were comfortable living out in the eastern suburbs almost certainly.