The Copenhagen Consensus Center does research on the costs and benefits of various policy approaches to global problems and provides information on which policy targets will do the most social good relative to their costs – acknowledging that factors other than cost/benefit ratios are also important. This is from their cost/benefit analysis on different approaches to biodiversity:
Translation: the figures on the right represent the economic benefit value for every dollar in cost. Looks pretty good to me: most policies considered give a lot of bang for their buck. The lone exception is “increase protected areas”, but the net cost is not that much. Seems like a bargain to me.
Many businesses subsidize some products through the profits they make on other products - why should policy approaches be different? You have to look at the whole mix of policies, not just the costs and benefits of each policy considered separately.