You could try to use the CNC Mill to create sections of a tool for brake ducts and then join them (because the mill doesn't look big enough to make a tool in one piece). You'd have to do some bondo work on the joints to make a good tool.
Then you could layup fiberglass over the tool. As long as it's a room temperature cure material you could even use delrin or similar materials for your tooling. Again, it wouldn't be rapid, but it would be pretty darn cheap.