Originally Posted by BearX220
MasterPark is the most expensive option but they seem to have the most shuttles.
I use ShuttlePark2 most often and they're friendly and inexpensive, but I've waited up to 25 minutes for a shuttle. They also are a mile or so from the airport.
Our experience is identical to what you've described. The complimentary water bottles that ShuttlePark2 hands out on the bus are a nice touch.
We have recently gotten good deals (e.g. under $100) staying at the Courtyard by Marriott in Tukwila and the Southcenter Hampton Inn because they have free parking. The parking is right out in the open, so it doesn't meet the OP's concern about parking security, but for a ten-day trip a decent motel room, breakfast (at the Hampton) and high-speed Internet are basically free.