If you go with your family as your staging area and they give you the transport to and from the starting and ending town, like CR said, your fee includes the camping and baggage. So no extra costs. I’ve heard various experiences about using the general registration camping but plenty of people do use it.
Otherwise a Cedar Rapdis area RAGBRAI team would be a good option. Or a team that stages near Cedar Rapids. Teams are usually in the $250-$300 dollar range (+ registration) and make the experience easier logistically then general registration camping. Des Moines area teams also work if you skip the family visit as the airport has more direct connections.