So right now we have...
1 box = 5$ = 5$ each
5 boxes = 20$ = 4$ each
14 boxes = 50$ = 3.57$ each

The issue is that I buy like... 200 dollars of prize box at a time, and would like better deals for buying more. This would also help convince people to buy more at a time, and therefore give you more money. I would like to suggest something like...

1 box = 5$ = 5$ each
3 boxes = 12$ = 4$ each
7 boxes = 25$ = 3.57$ each
16 boxes = 50$ = 3.125$ each
34 boxes = 100$ = 2.94$ each
72 boxes = 200$ = 2.77$ each

This also offers better deals on smaller numbers of prize boxes... the idea being that there's a huge difference between buying in bulk and not. While this would be giving more out per dollar spent, I think that's a good thing, as it makes the F2P look nicer when there's a bunch of spammable junk on the auctions.