Actually, 'cost benefit' doesn't generally (in my corporate experience) mean 'bang for your buck'. It's short for 'cost-benefit analysis', which is when you compare the costs of something to its benefits.
For example, if it will cost a factory $5,000 to implement an improved safety feature that will prevent an average of 10 amputated arms per year, the 'cost-benefit analysis' is that for a mere $5,000, the company will prevent 10 employees each year from losing an arm. That would weigh heavily on the 'benefit' side of the equation, as I'm sure everyone would agree.
On the other hand, if a company implements, say, some new mail handling procedures that cost $50,000 but save only $500 per year, the costs outweigh the benefits.
IOW, 'cost' isn't an adjective modifying the noun 'benefit'. Both are equal adjectives modifying 'analysis' (which might be absent as the understood noun).