I've been hearing for years that artificial gems (diamonds, rubies, moissanite, etc) cost a 'fraction' of the real thing. Is this true? If so, where can I as a consumer buy a handful of this stuff?

Note that I don't want jewellery-grade gems, I realise that would cost a lot simply due to rejects and labour to cut / polish. I just want stuff I can mess around with for hobbies and crafts.