I paid $100 to purchase a training plan from trainingpeaks.com last year, and defintely thought it was a worthwhile investment. I used it to train for Cycle Oregon, a week long ride around Oregon. The plan that I followed was Joe Friel's Experience Plus 501 Tour plan.

One thing that's different in training for a tour vs. a century is that you want your body to get used to doing back-to-back long rides.