Sry if this is annoying, but I helped start a Rugby club at my school and we need balls, so if you know anywhere where they give a discount if you order 10+ or something, let me know by PM or here thanks! I'll give out whatever rep i have too thanks!
There should be many places where googling "rugby ball" would get you the answers. One place here in AUS is http://rebelsport.com.au/?action=list&category=180 but I don't know if it is the "cheapest". Currency is AUD ($1 AU = $0.75 US).
worldrugbyshop ruggers Matt Godek rugby try these places - they should have some discounts available. Also hit up the US Rugby Football Foundation, as they give kits and balls to high school programs.
anyone know of any online sites that have a Waikato NPC kit? worldrugbyshop.com used to have one and they don't now. I was told in an email by them that they would be available soon, and that was in the spring. I've gone to Waikato's website and seen them in the club shop, but I didn't know if anyone knew of an online shop that was in the US that would have this kit.