instamold/bluestuff. easy, reusable, and a great start for low prices.
it is a tiny bit tricky to start off as it sets very quickly, but as it it reusable, it only takes a couple of hours to get the hang of it. such small items are a great start to learn how to work with it.
I am in no means an expert on casting, but I've used this stuff for some time now, and it makes for easy copying.