What cruise line is best and cheapest to travel with a 3 year old?

proudmom asked:

We have never gone on vacation with my 3 year old son and would love to go on a cruise. What cruise offers kid friendly activities while also being reasonable priced? Disney seems so expensive. We’re looking at traveling the end of August 07 and it would be for 2 adults and 1 child for hopefully 5 nights. We live in Colorado but would fly to Florida, etc if we got a good deal on a cruise. Any help would be appreciated. thanks.