Seriously. I can't imagine the set of parents who buy an iPhone/iPad for their kid but won't spend the $100 to let their kid build with it is a large set--in fact, it's probably empty.
Yep, even if they have to buy a Mac ($600 for a Mac Mini), that's still cheap. I'm glad my parents spent money on my "software habit," which has given me a lifelong valuable skill. I'd do the same for my kids in an instant.