I don't know how they will charge you but if you can't do it but you know what you want then getting someone else to do it is really the only option I can think of. Did you look around for the best price or are they the only ones who can do iApp's? If you know anyone personally who could do it then you could try to figure out a deal between you both, for example 60-40%.
I would start go with the demo then charge for the next levels. Hopefully this will get people hooked on it.
Hope it goes well
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If you dont truly believe in your product, then it's not worth selling