Road trip up the West Coast! Chico CA to Seattle WA

[jon]

Hey everybody!

My two friends and I are planning a road trip up the west coast and have planned to dedicate a max of 6 days to the journey. Starting around January 4th, we would really like to drive the 101 from Chico, CA all the way up to Seattle and sleep on or near the coast two or three times along the way. The three of us are college students and are pretty short on cash so we are hoping to put everything towards gas and sleep for free or as cheap as possible.
The drive will be made in a Suburban and we are thinking we will have plenty of room in the back for sleeping 3 people.

Is sleeping in the car even a good idea?
Are there any camping locations located off the 101 (free or affordable) that would work?

We are a little unorganized and are looking for any guidance we can get.

Thanks!