Removed random extra costs from flatpacks.

First nerf, now slight buff to previous system.

Extra costs were impeding mechanic's ability to make proper machines, leading to them being basically useless in terms of deploying flatpacks.
Considering these things are metal and glass to build by hand anyways, the plastic cost is enough in my view.
They're also expensive in terms of the materials they already require. I'm not entirely sure about this, but it seems like a good balance of rarity (plastic) and usefulness.