Sourcing Plastic Molds

Hello,

I was wondering where a good place to source moulds to grow the fungi materials in or alternatively a mold that isn't a plastic one. What have you all used before?

Here in Australia getting thermoformed molds made (with tooling cost) can range from $1000-$5000 for even small orders. Only looking to grow some shelving units that price is way to high.

Thanks,
Ben Sharp