Platypus, I haven't used these courses personally, so I can't comment meaningfully on scope, but I recalled reading that the CTY science courses are based on another curriculum (Plato), which can be purchased much less expensively through the Homeschool Buyers' Co-op. I think this was the discussion I found that information in originally. If you go the CTY/Plato route, hopefully this can save you some cheese.

http://giftedissues.davidsongifted....e/Re_Experience_with_CTY.html#Post211633

Hopefully someone with experience in the science courses can chime in!

What is to give light must endure burning.