well for the model you can use from clay to a modelling resin.
to make the cast you can use from plaster, ceramics, pp plastic, or hdpp plastic.( but with both plastics you will require a vacuum former)
then when you have the invese shape of the cast you pour inside any material you want. the most common shit is plastic but it melts at very high temperatures so its not recommendable to use an oven or some shit like that. you might want to use a melting bucket.
casting stuff is expensive.