High school and College are the NFLs D Leagues already. The NFL doesn't have to pay a dime to have their players already get developed. So again, why fix something that's not broke?
People coming to a meet and greet for a known Packer name does not equate to the tens of thousands that would be needed each game for each week to make some awful D-League team full of absolute nobodies to just break even on salaries. There's no way there's enough interest and money from the fans to make it financially worthwhile, and that's what matters to the league, the money.
Look at how fans even hate having to pay for and watch pre-season. The casual fan hates those games. They are full of scrubs anyways. You think a league full of the worst of them is remotely financially viable? Dream on.
I think you're way off on your estimate of cost for the team. Travel, hotel, and food costs are massive, NFL teams travel with anywhere from 120-160 total people. I'd think these guys could likely get by with 85-95. But your total budget won't even cover these items.
I just think the NFL is already on the down slide. Granted, it's from an unbelievable high point. But the ratings are dropping, the participation in youth is dropping, the game is changing to where people think it's too wussified and are losing interest. it's just too late in the game to start up a D league. Not when there's already an extremely comparable thing already in existence that's free.