There are pattern making resins that 1) don't shrink much 2) are hard as any low temp metal. But many of these compounds
have very toxic bases. The low temp metals I would be careful of; use them outside if possible. I use one of these for the occasional
chamber cast.

Consider traditional foundry or investment casting. If several of you are in close proximity you can pool your resources. Making the models I do, a foundry is integral to my work. Foundry work need not be super expensive nor complicated. You can scrounge
raw materials and make a setup for next to nothing if you really want to. I built my own furnace with a capacity of a #16 crucible
for not a lot of money. I can use a #2 crucible in it as well. I can melt that #16 full of aluminum in 10 -15 minutes. If you want to do
bronze as it flows better you can do that also. You'd be surprised how easy it is. Safety is key however as with any molten metal- it is not a toy. It can and will hurt you ( or worse) if you are not careful.

jerry