As a learning exercise, I'm sure you'll get a lot out of building an entire humanoid figure, uv mapping it, texturing it, and rigging it.  I couldn't build a very good person from scratch, let alone rig it to bend very attractively.  From a more practical standpoint of building yourself a manbat that you could quickly use, I'd still argue that you'd be better off making a morph for an existing figure.

This is probably about a half hour job morping M4's head in zbrush, which you've already commented that you can't afford.  I don't know whether or not you could do the same in sculptris as that program tends to like turning things into triangles and adding geometry willy nilly.  Still, with this headmorph done,  I think much of the rest of the creature could be accomplished by scaling m4's bodyparts.  Broad chest,  skinny waist, short legs, long arms. You'd then have to texture it.  I don't know that there are many free tools adequate to that task, as having deformed the mesh quite a bit, I'd want to do my texturing directly on the model it to minimize the stretching of the texture.  If I tried to create a texture for this noggin in photoshop, it'd wind up looking warped all to hell on those ears.  Painting directly on the model would minimize that.

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