[labawi]

If you add opportunity cost and renting cost, you are double counting.

Assuming you can repeat your "totally legit" setup transactions until you succeed, with minimal cost other than rent, you would need to take more than either the opportunity cost (otherwise it's better to just mine), or the renting cost (otherwise you're still losing money).

[Rodyland]

Adding opportunity cost and renting cost isn't double counting.

Opportunity cost is the foregone block rewards that you lose because you didn't submit your blocks, because you were holding them hoping to build a long enough chain to double spend. When you fail, that reward that you would have earned is gone forever.

Renting cost is the actual $ outlay that it costs you to rent the hash power necessary to perform the attack.