Well......
If your going to trail ride it and not in the sand I think you should get a four stroke in the 200-250 range.
I like the Honda CRF230R as it is fairly light, handles very well, has electric start and they are affordable.
Here is one I found on C/L in your area:
http://roseburg.craigslist.org/mcy/3122609719.html
Another great bike is the Yamaha TTR230.
Here is a link to it:
http://portland.craigslist.org/clc/mcy/3155815976.html
Let's say that you wanted to ride it in the sand or wanted to ride it on a MX track.
Then I would say get a 250 2 stroke.
It will take a little more riding experience but they will offer a lot more performance.
One of my employees had only rode bicycles before he came to work here.
I picked up a Husqvarna CR250 2002 that I thought was a little much for him.
We went out to the sand dunes and much to my surprise he did great.
He rode it for 3 years and loves that bike to this day.
Here is some good examples of a few 250's in your local area:
http://eugene.craigslist.org/mcy/3141781784.html
http://eugene.craigslist.org/mcy/3139894651.html
There are many others as well but I would look for 95 and newer KX250, CR250, YZ250, or RM250.
In the end, you have to decide what's right for you.
I would stay with as new of a bike as you can afford.
Anything past 10-15 years old starts getting dicey when trying to find parts.
It use to be that the manufactures had parts for decades.
Now, after 10 years they loose interest in supporting them.
If you want to take some test rides I'm sure I can find a few things around here to put a smile on your face.
Thanks!
SB
If bikes are for kids I'll never grow up.