Buying a Bonsai tree in a shop is nice, but wouldn't it be much cooler to do it yourself? A great way to start growing Bonsai trees is to buy a starterkit and style the tree into a Bonsai. A starterkit can be purchased at many (online) Bonsai shops, but you could also choose to buy only a young plant at a local gardencenter.
This article (including a movie) explains the steps to grow a Bonsai tree from a starterkit, all by yourself!