Maybe it's a Canadian thing, but a small enough amount of purple heart shouldn't cost that much, at all. I picked some up at Woodcraft (big specialty wood working chain) and didn't pay anywhere near that much for a block 2"x2"x12". Of course, that was a little while ago, but I can't imagine it going up so much in that time.
If you do some web searches for it, you can likely find it on the auction site, as well as some specialty wood suppliers. Do you have a preference between wood or synthetic? You could go for pink G10, Micarta, or the dyed woods-maybe check some of huge knife supplier's websites. If all else fails you, give me a holler and maybe we can get you some of the purple heart I have. Would hate to have your daughter go without a super cool knife for lack of scale material
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Jeremy