Well, it doesn't cost exactly zero, as there are costs to handling the paperwork, etc. And if you look at economy-wide costs, it distorts economic decision-maki

Well, it doesn't cost exactly zero, as there are costs to handling the paperwork, etc. And if you look at economy-wide costs, it distorts economic decision-making, which definitely has costs. But what the OP is referring to as "cost" would be better said as repealing it would bring the budget $130 billion closer to balance (through increased revenue). But if you insist on that distinction, make sure not to call (for example) tax credits offered for renewable energy a cost, either.