I've had my eye on this LEGO robot kit for my kids, at $49: http://meetedison.com/

I'm also excited about the possibilities of expanding LEGO kits with 3D-printed parts as print resolution continues to improve. You can already achieve some cool things by gluing LEGO pieces to 3D-printed parts, but that seems like cheating. http://www.thingiverse.com/thing:403