That's a good idea in my opinion, although I think the actual crafting bench should only be 2x not 3x cost. Inventory crafting though, yeah something in the region of 3x-5x the cost to craft sound alright, but once again the inventory crafting, at least its first stage, should only be tier0 items. then possibly have an upgrade for it to unlock more items to craft again with the increased cost to craft. for example at tier5 or 6, just like unlocking some thing like the oil processing or any other tech, you could unlock the basic inventory crafting(tier0 items), then at say tiers 8 or 9 unlock an upgrade to advance inventory crafting.