When we have to stash a car, we usually use one of the MasterPark lots. There's always a coupon available a through Alaska Airlines, and we get Alaska miles for staying there.
I'm sure they're not the cheapest, but we've never had a problem with a car parked there. Pick up and drop off service is pretty good; when returning you just need to be sure you get on bus to the correct lot (each MasterPark shuttle goes to only one lot).