Legacy Learning Systems has several, at home, music curriculum series. Two years worth of lessons for under $200. We have the guitar and my son, although 15, is picking up on it incredibly fast.
It is just like going to a lesson. You watch the video, then you practice the rest of the week, with all the materials needed for keeping track, etc. I HIGHLY recommend it. I am planning to start my seven year old and not sure it would work for a five year old, but most likely if you were there to help him. I figured it was worth a try, if they stick with it, I can look into further lessons, but if they did not, it was not a lot of money wasted. Compared to $20-50 an hour, time and gas saved, it is well worth it.