[lukevanoort]

If ChrisH comes across this thread, you'd probably get the best information from him. I don't really know much about working with composites, but have you considered wood? I imagine you could make some nice and light sheets with CF and balsa (or birch or hard maple if you want some more strength). The low price requirement kinda puts a bit of a limit on what you could use (polycarb and garolite, for example, get rather pricey in large amounts). Industrial cardboard can also be quite strong... I imagine a healthy diet of CF would make it even stronger.