If you're crazy enough to try doing this legit, or don't want to waste money repeatedly selling Kurumas, the Criminal Mastermind challenge will award you $10M if you manage to complete it. The Loyalty and All in Order challenges (that you can complete simultaneously) will also award you an additional $1M each.
However, that does mean doing all five heists in order (including all setup missions), on hard, with the same crew, with no one dying. No small feat.
For anyone willing to try, this handy guide should be a big help: http://gtaforums.com/topic/779754-criminal-mastermind-in-dep...
(all credit to GTA Forums user NeoLedah)