8 months ago - Shurenai - Direct link
Either steel is hard to get and costs are adjusted accordingly, Or steel is easy to get and costs are adjusted accordingly.

A door stops some zombies for a short period of time. A gun murderizes hundreds of zombies; Guess which is more impactful to your gameplay?

In short, This is game balance. Gun does a lot, so it costs a lot. Door does little, so it costs little. It's not about amount of material actually required to make the thing based on size/volume.