One of the nice things, is that Oregon often has their scales closed, but still open (some other states do this too). When I come across these, I often will make a quick stop or U Turn to go back and weigh. Its free! I like that too. Most truck atlases have these listed where they are.
When I have the time and no one waiting, I have actually split my trailer off and weighed the tongue weight and axles separately. As well as my motorcycle, with me on and off it. Talk about; "a bit of a surprise" with my own personal weight!
Free Places I remember;
Lakeview, OR ~ (US Highway 395)
Marcola, OR~ (State Highway 126)
Sisters, OR ~ (State Highway 126)
Springfield/Marcola, OR. ~ (State Highway 126)
Ashland, OR ~ (State Highway 99)