Cobol programming is a skill that is trivially taught. Any student with a Cmpt. Science degree from a credible institution, given a curriculum, can learn any programming language in a month with a bit of focus/appropriate curriculum. Can pick up the necessary frameworks in a reasonable period of time. Then it's just a matter of teaching them the line of business, and the practices and procedures.
I would claim that, given twelve months, you could teach a cohort of recent Cmpt. Science graduates all the skills they needed to be successful in any Insurance/Banking/Finance programing environment.
And these are developers that you can then pay a very reasonable salary - say, $150K/year - which is $75/hour, not $300/hr, at the cost of 1 year of salary as they come on board, come up to speed (say at an out-of-college salary of $100K/year.) - You need 1,000 of those developers - that's an up-front cost of $100mm, at which point you have your developers.
Compared to a multi-billion dollar transition cost off of a mainframe, I know which one I would chose if I were the PHB.