I wanted to build some mines, but the cost seem way too high to make sense. Like 7500 recources, for a +10 per month return (!).
So it would take 750 months (or 37.5 years) just to get back the recources you invested to build the mine, before you even see any profit at all.
Or is this just another problem, where the tooltip is incorrect and the actual increase per month is higher?