What does it cost to put an app on AppExchange?

To list on the app exchange you need to be a partner. If the app is a paid managed app you will have to pay the security review fee. Unmanaged apps cannot be listed IIRC Additionally you will have a Revenue share (something like 25% now I think) with SF. The cost would be $2,700. The impact on revenue would be 25% of collected revenue from the app. So not a cost but would have to be factored into your pricing or accounted for in your business forecasting. (Depends on your definition of cost)