You can easily pare down those costs. Bring your own towels and tent. Eat at restaurants or buy food rather than the tour's meal plan. You would have to eat anyway that week, regardless of touring or not, so it's not really fair to count that in the costs. As others mentioned, usually the tour organizers don't charge extra for baggage transport unless they are having to deliver your stuff to local hotels. Generally the baggage transport to camp sites is included in the overall fee for the ride.

Regarding the rental car, you could explore other options. Take a bus, and have them carry your bike in a box. Or try to carpool with other riders from your area. Eg, Cycle NC has a message board on their website, and many of the messages are from people trying to arrange transportation and carpool.