The last two times I've driven to YOW (usually I take the #97 for $3.20 R/T), I've parked at the offsite lots. First at Park Air Express (now called "P4"), the last time at Park N Fly. The latter is more expensive but the bus is nicer [I know, so what] and the lot seemed in better order, although I got a closer space at PAE. In both cases I got quite quick service to the airport, and acceptable service back.
The third-last time I went, I parked in the Regular lot (now called P2?) at $11.50/day and I think it took just about as long to get from my vehicle to the terminal, as with the offsite guys. Anything short of P1 or P3 ($15.00/day) is probably just as fast to go offsite. (Reminder: this is YOW I'm talking about).
andrew