That's ridiculous to need to pay extra to use the arena. You pay your board, you should be able to use it whenever you'd like. I have honestly never heard of a barn charging extra to it's boarders to use the arena.
Either way, $450 in my area at least would be considered cheap for full board. It really does depend on your location, as well as the facilities offered. I live in a pricey area and board at an extremely nice barn, with very reasonable rates, and excellent care. I pay almost $1000 per month for two horses for semi-self board. I prefer semi-self since I am there every day anyhow and enjoy looking after my own horses.
IMHO I don't think barns should charge extra for blankets on/off, fly spray, etc. However, I do understand why BOs charge it, especially on a horse that may be difficult with such tasks, the BO has every right to charge.
I would look around at other barns in your area to get an idea of what is reasonable. What may be reasonable in some areas, could be considered pricey to others, or cheap to others.