Assuming you are using water-based clay, in sculpting a life-sized bust, there is a balance between letting the clay dry out just enough to support its own weight and not letting the clay dry so much that it is unworkable. If you can sculpt the basic form and then let the clay set up somewhat, you may find your task easier. The harder clay supports the weight better. For a faster (and slightly more advanced) technique, build the bust up hollow (about 1-2 inches). A hollow clay form can also be fired fairly easily, while firing a solid life-sized bust poses significant challenges for most basic studios.
If you are using an oil-based clay, I would have to agree with the prior posts: a single trip to the hardware store should provide all you need for a good armature. I generally use 1-inch plumbing pipe set up in the form of a "T", and then massed out with whatever I have on hand; sometimes old newspapers and duct tape, wrapped in flexible "gutter guard", rabbit wire, plaster lath, or any other mesh to give the clay something to hold on to.