As Don Says It will be expensive, if at all possible.
I question why you want or need to do injection moulding?
I work for a University & we did have the IM machines, but the dies are always metal to contain the pressure.
Nowadays all the rapid prototyping is CNC cut/lathed, or LASER cut, or 3D printed, but knowledge of 3D design is needed, as is access to printers, but there are companies like Shapeways if you don't have the printers etc.
If you can produce masters, then you can produce sillicon/RTV/Vulcanising rubber moulds and produce your parts in resin, plaster, etc.
Let us know how you get on...