When it comes to transporting a car to or from the city of Portland you may run into some difficulties if you're not moving it from California up north, mainly because there aren't really any east-west interstates that are popular with auto transporters that run into or out of Portland.
I-84 is really the only major east-west interstate going into Portland, but the problem is that is doesn't really go through any popular auto transport locations. Carriers and customers alike move a lot more often through major metropolitan areas; if you're moving north along I-5 from somewhere in California up to Portland, your prices will probably be cheaper than if you're moving from somewhere in the Midwest. I-5 is a much more popular auto transport corridor than I-84 because it runs through so many more major metro areas. Is it impossible to ship to Portland from back east? Of course not. But it may cost a bit more is all.