Transportation

I will be taking care of 5 children, in addition to my own 4-year-old, and am wondering what everyone does in the event they need to transport the children. I'm thinking of buying booster seats for everyone for the Suburban, but that will be a bit spendy. Then again, switching car seats back and forth between the parents and my vehicle doesn't sound too ideal, either. What do you do? My 8-year-old will be going to and from school with a neighbor, but on the days when she works I will need to take him and pick him up.