a couple things on injection molding and nylon.. I don't want to burst your bubble, but do some homework first. I can tell you this.
You can't take a bunch of rope and chop it up and put it in a sauce pan, melt it on the stove, and pour it in a mold like lead or pewter.
- Aluminum is considered to be the cheap mold material, and ceramic is a LOT HARDER to machine. Plus, with molding, a conductive mold material is good, because you can better control the temperature of the mold.
Next up, nylon is a super mega royal bit¢h to mold. OK there are probably things that are worse, but nylon has to be dried for HOURS before molding - down to 0.1% moisture or less, heated to 450ºF-500ºF, and injected at pressures around 10,000 PSI..... and it loves to scorch and burn, and smells horrible when it does....
NOW, they do have bench top molding machines. I'm not sure what the price is - I know they're not hundreds of dollars, but they CAN do nylon. Here's one...
If you want to mold plastics, I'd look in to casting urethanes. You'll get good results, and if you've got the kind of budget that is conscious about the cost of a block of aluminum, I really think that you might have trouble justifying the cost of the equipment needed to injection mold thermoplastics to even the lowest level of quality. Then again, some people have reportedly made injection molds out of epoxy (not Devcon 5 minute, mind you)
The good news is, however, that this IS a forum with a bunch of machinists in it... I'm sure somebody could help you get the parts you need!