Here are some inexpensive ways to get into casting parts. If there is interest, I'll post photos. I've used these methods for slush molding an entire body as well as small parts.
Permatex Red High Temp RTV Silicone Gasket Maker
Permatex results in a fairly strong, flexible mold and will take fine detail. If used by itself, this must be applied to the master in thin coats. Can be mixed with flour (my preference), sawdust or Durham's Water Putty to speed curing and allow thicker coats. Flour or Durham's (a relatively strong plaster) shouldn't excede about 1/20th in volume or the mixture may not harden properly. I mix on a hard surface, repeatedly spreading the flour/RTV mix as thin as possible. This seems to speed curing (it may absorb water when spread thin). I don't go over about 1/4 inch thickness with each coat. Sawdust should be screened down to near-dust size particles for best detail. Coarser sawdust can be used for outer coats for strength. The Permatex will cure regardless of the added amount of sawdust, but too much may weaken the final mold. I've used a 1-to-1 mix without problem. With either additive, the Permatex still likes ambient moisture to harden. I use a plastic box on a plastic surface with damp paper towels under the mold. I've read that RTV in general will harden faster with heat, which makes sense. If using urethane casting resin, mold release agent may not be required, but may help extend the life of the mold if it has fine projections. It stretches well, but doesn't seem to compress.
Urethane Casting Resin
I've only tried three types: Alumilite, and MicroMark CR-300 and CR-600. I strongly prefer CR-300. It has a short (a few minutes, more resin means faster hardening) but workable pot life, doesn't smell as much, takes fine detail and is very easy to carve and work when fully cured. It is similar to styrene, i.e., not very brittle. I use thin fabric as a way to make thin castings stronger, like using fiberglass cloth to lay up a surf board. The CR-300 soaks in and through, so a trimmed sheet can be positioned in the mold before pouring the resin. Work out any air under the sheet as much as possible.
Durham's Rock Hard Water Putty can be using for casting larger simple objects, too. I have mixed in waterbase acrylic paint slightly diluted with water to add strength and workability. Once in the mold, tap or vibrate the mold. This will liquefy the Durham's to help fill the details of the mold, but doesn't seem to cause any problems with hardening. Hardening will take overnight. This is a very cheap material.