3D printing being a wide field ;-) If its very high detail would have though SLS or DMLS would offer the resolution possibly requiring intermediate steps to make a working mould, sure can get SLS baked to short run injection mould level.

Milling into wax or foam and then investment casting from there.

Spark erosion into hard steel for longer run moulds.

No way of getting round that it is a lot of hours on very expensive machines, once you have the moulds, small as they are ,raw material is going to be pence per shot.

Is this one of these artistic ambitions meeting the cold light of day moments though.

"If you only knew what it was for you'd bite my hand off at the chance to become a partner!"

Hay tomorrow, always tomorrow....

If its a sure fire winner, producing moulds goes from expensive to scary expensive , producing parts is cheap, someone will bite your hand off to put the money up to have the moulds die sunk, which would then give you a realistic budget to work from.