A worthwhile book to study may be "Cutting Costs in Short-run Plastics Injection Molding" by Morgan Industries. Includes an approach to building molds for short runs using high temp epoxy in a re-usable aluminum frame, as well as more common approaches. The epoxy method drastically reduce tooling costs for short runs. Plus lots of good information you'd need to do short runs on small manual and semi-automatic equipment. About $32 plus shipping, I think. Just got my copy. Don't know much about their machinery offerings.
http://www.morganindustriesinc.com/p...ding-guide.htm