Oh yeah, it can be expensive to make art!
Castilene is pretty good as a wax/clay hybrid....it's similar to clay when warm, and similar to hard wax when cool. You might enjoy it! It gives you more control than Sculpey...because it won't lose detail when you handle it with your hands or set it on a desk. It also doesn't need armature.
Because it's soft when warm, you can use heated tools to carve in it, and sand it to a clean finish with sanding sponges. I've seen artists get an amazing finish in Castilene, but I'm not capable of doing that. That's why I use hard wax....but it's just a preference. Every artist uses whatever they like!