2 coal
2 iron plate
1 copper plate
4 STEEL => ~2 coke + 8 iron plate => 2 coal + 2 wood + 8 iron plate

total:
4 coal
2 wood
20 iron !!!
2 copper
without energy cost for production

This don't make sense, I play with bitter and this is just ridiculous. It's way too much expensive, yellow are a little less effective and yet cost 5 times less iron. I just think I should stop produce it and just stay on yellow. I go search for a iron deposit I still have more than 75% of my initial copper field. The mod use too much iron in early. In vanilla there are already quite expensive but as you put 1 iron plate for 2 iron, this is uber too much. Cost need to be at least divide by two for consumable ammo. Or increase the magazine size of something.

K2 has a 3X larger rifle magazine size. But I understand that the cost can really be expensive. We will change this a bit in the next update.

To be clear, this is good but tower happen to die a lot in early (no robot-port to repair) so loosing a tower with 5-6 ammo is very costly and 5-6 will not last so long. My complain is that the gap between tier 1 and tier 2 is too much the bonus are too low (well no, bonus is ok but doesn't match the additional cost), there is currently no point to build red but we got the technology quite early.

Anyway, thanks for your consideration. The magazine size is a nerf in fact. At least in early game.

lol, I checked the next tier:

tier 3 => tier 1 + 4 uranium
tier 4 => tier 1 + 4 imersite crystal

haha this is SO CHEAP compare to red one, there is simply zero gain to do red because tier 3 and 4 have same base damage, follow your rule

tier 2 should be => tier 1 + 1 steel (4 iron raw like tier 3 and tier 4)