Materials costs are zero. The main advantage in working with miniatures is that we need very little in the way of materials. I love using eucalypt wood on the lathe but these trees don't grow straight. It doesn't matter because I generally only need a piece that is 3-5 inches in length and, even on a twisted branch, I can often find a section that is straight enough to use. Even if I need some square-sectioned wood, I only need a small piece, and can get those by fishing off-cuts out of a bin on a construction site. I work in an electrical store and a lot of large appliances include lengths of cheap wood in their packaging. Whenever one of them is unpacked to go on display, the timber comes home with me instead of being tossed in the bin. Everything I do on the lathe costs me nothing except time and I'd rather spend my time making stuff rather than watching TV or playing video games.