Okay so this may be a little specific, but we're flying in/out of Dulles pretty soon and need a plan for parking. We're several hours away so getting a ride doesn't seem reasonable. We'll be gone for a few weeks so even the economy lot ($10/day) will add up quickly, but monthly parking there isn't cheaper. I considered a rental car both ways but we're not flying with our carseat so that would create a whole separate issue.

Seatac used to be our main airport and there were tons of cheaper park n ride type things with big lots and shuttles, but all I can find for Dulles is stay and fly type things at hotels, and we don't need somewhere to stay!

Any savvy travelers with a better idea?