Rental /One way Airfare

What is the Cheapest way to rent a car in Portland and return it in San Fran? I see all types of great rates you can bid on, however they are all pick up/return in same location (We would love a convertible but,do not wish to rent a car for 2 weeks for $600). I am also looking for the best way to get ONE WAY airfare's for cheap. Due to it not being ROUND TRIP TICKETS, the price bumps up big time.

If the round trip tickets are cheaper than the single ticket then do as I did and purchase the round trip ticket but don't use the return. It may seem mean to leave an empty seat but it is not as mean as bumping up the price of a single ticket.