well, the chain we're working with appears to survive on the "cheaper than the big boys" motto, so I would suggest doing an 8 or 9 dollar large (if the ingredients don't force them to take a loss). That price point brings a better product (they do 5 dollar large 1 toppings currently for carry out i believe) and it's still below the Papa Johns 10 dollar for a large 3 topping I think. those prices are before delivery.
anyway, that's my contribution since I order papa johns online a ton
maybe have them get a BOGO (buy one get one) promotion IF the person comes in dressed up as... something. anything.
kinda like Chipotle gives away a burrito if you come in with a tin foil costume.