I bet it's that high to weed out the potential scam artists. If you're going to try to scam an NFL player, you're going to have to pay for the privilege. Makes sense to me.
I would think the background check and required $4 million of liability insurance would weed out the scam artists pretty well. This is just for the NFLPA to make money. And the pool of potential clients is quite limited, especially if you're in a place like Denver.