Your seating capacity has a big influence on what prices you can charge. Since you're doing well in DIV V and you only have 4800 bleacher seats, you should optimally set your bleacher price at $11. That should get you close to selling out those seats. $12 is a possible but then you won't sell any seats for any future expansion during this period. When you promote to DIV IV, you'll have to readjust by looking at teams arena prices for your new division.
If you build Luxury Boxes for DIV V, aim for 5-8 but you'll have to price them between $800-$875 to sell out depending on how many you have.