i think ur better in buying a used asic miner than a using the graphic card method, i dont know why people using this methods, already a 80 asic miner have more power than my geforce 1060.
mini is worth, the problem is more the price u pay for engine, like some guys want use a water power so they pay 2 Cents for a kw/h in Austria and not like regual people over 20 Cents.
in the past i had a list with costs per Bitcoin, like in Venezuela u pay 800$ for mining 1 BT