I got lucky and won it a few years ago--the only time I've participated. I had a lot of adult supervision making my bow.
You can start as early as Wednesday or Thursday (check with Pappy to be sure). Cost depends on whether or not you bring your own stave. If you buy one, depends on what you buy. Other than that, I think it's just the tournament fee.
I want to do it again, if I ever get the time. Lots of fun. That year I shot the "Ironman" (longbow, recurve, and selfbow - one that was already finished). I shot my best score with the bow I'd just built - go figure!