Probably better to learn that lesson going from Div V to Div IV, rather than later when it'll cost more :)
For the record, saying that you should base your prices on "other promotees" is incomplete. Really, what you need to base it on are "other promotees in the same division. This is because fans will be more likely to come to a higher division game and more willing to pay higher prices, much the same as there are greater attendances and higher prices for an NBA game than a college game.
To get a better estimate, what I'd actually suggest instead is whenever you promote into a new division, check out ticket prices for teams that are already there. Set your prices slightly higher than a team that has a similar size arena to you, and seems to be almost selling out each seat type.