Ask HN: Tips on negotiating a price for an app re-branding?

We're currently in negotiation with a big soft drinks manufacturer to re-brand our mobile app for one of their brands for use over a 2 month period as part of a drink launch campaign. The target market is a very large Spanish speaking country in South America.

Does anybody have experience with such white labelling deals? We were thinking some up-front fee for the re-branding and translation effort, then some amount per install. There is no back-end overhead on our end, 100% client side, so we don't have to recoup server costs.

Any advice on a quantitative approach to get a justifiable figure for the initial negotiation amount?