You can have the master/plug cut from cheap and easy to cut materails like MDF. This can be sealed/painted to prep it for molding.

You can also have a mold directly cut but the material choices can be expensive if you are trying to pull more than a few parts. If you want a high grade surface on your parts then you need a material that can be cutt and polished. Your options will be aluminum, tooling boards, and glued stacks of Corian. If the surface isn't super important then you can cut a mold from MDF or syntactic foams, seal it with resin, and pull your parts. This type of mold doesn't produce very many parts.

An aluminum mold set (fuse, stab, wing, joiner) for a 60" plane can easily cost $10,000.