Pricing information for Apps

[TheBaldr]

Me and a friend run an independent game app studio as side income. We were approached by a business to create an service app for them that they are going to distribute free to their customers(They have 60,000 paying customers). The app is not a problem for us, but we just have no clue what to charge. Is there any place that has more information on this? We want to charge a one-time development fee and an annual fee to keep the app updated.

[InLikeFlint]

I say you charge a startup for the app, and then possibly charge perhaps a percentage of the sale...assuming that it will make quite a large amount of money