That trade back was an extremely rare situation. I doubt a similar trade has ever involved that much money. Just because DL got an incredible deal on that does not mean that second round picks are now worth millions.
2nd round picks have been worth millions for a while. Getting three million in a late second-round pick swap seems insane even to me, but it also speaks to the market. A pick isn't changing hands for anything less than a million if we're talking strictly money and no other assets.