After some initial problems (pipes actually don't cost copper, I thought I was stuck right at the beginning until I justr tried to place it, it doesn't actually cost anything.
This is the most time I've spent on a jam game, really well done! I love tower building/factory and tower defense games, and you combined these two nicely together! Really cool to see so much content implemented in just 3 days.
I've encountered some issues after playing the game for a while, e.g. the silicon drill requires siliconbars, which I can only smelt from silicon that I would get from the silicon drill. Somehow I got around it by temporarily having negative Siliconbars :D Also The NutsBolts don't produce nuts and bolts, it produces small batteries. And the name of the selected building on the info window in the bottom right is not updated, only the prices etc.
Awesome game! Loved it.