Depending on where you rent your car from, you can return it at UO. Not sure what the rental company is or where in UO it is, but look at the transportation sticky or do a search and you will get the answer pretty easily. I know others have asked and answered that question.
I wish I was more helpful then that, but since we always drive not fly I just don't know. But check out the sticky and you will get those answers. That way you won't be paying any parking fees.
Also if you drive, you can make a grocery stop to get breakfast foods, snacks and beverages for the room to maybe save some money.
Good luck!