When you transport firewood you are also transporting insects and fungus at the same time. Sudden oak death if from a fungus being spread by people and decimating much of California's trees. Add in Asian longhorned beetles, bark beetles, California oakworm, and pitch canker.
I buy wood at the campground and either burn it or leave it there. I pay on average $4 for a bundle. It makes no sense to haul firewood on a $100 rack to save a buck.
Want to really save money, don't buy bottle water which is not healthy to drink either.