Most importantly THANK YOU to everyone who has responded.

Many great ideas and suggestions, so I now really have a better idea of options. Much appreciated. And I welcome more....

With regards to a car - my sister is a single Mom with 3 kids, (2 are teens), and 1 car. Because I will be working a portion of the time I am there, I will definitely need a car, and (will also) probably stay in a hotel. It is just easier on everyone. So I will need a car in Seattle.

As far as the rental car charges go, again - I am working, and would legitimately fly into one city/out of another UNLESS it is cheaper to fly between them. Then I would use a completey convoluted official formula by which my company calculates personal expenses from work expenses..so I would only pay the difference - or - do away with the hassle entirely and use free days, which allow for a one way rental. So costs do not have the effect on this trip that it might a strictly personal one.

All of which may be moot as it appears the trip may take place in late October, which, if I am reading everyone's posts correctly - moves the risks of snow from possible to probable.

And as Mr Sophie LOVES donuts and HATES snow - I see the Greater Portland area winning out over Crater Lake should that happen!