How do you quantify the cost in computing power with IOTA relative to the financial cost of a transaction fee. It seems that if you are forced to be a miner, then you are paying a fee in terms of compute power but are not aware of exactly what that fee is. What if you turn off you machine? How long must it stay on to ‘mine’ other peoples transactions?

It seems that with bitcoin you can pay a transaction fee AND also choose to be a miner in order to recoop some of that fee. With IOTA you have no choice? Is that accurate?