Well done for creating the app. Great question.
Regarding setting the price: I would try run a survey with some screen shots that show the game and it's purpose/experience, and ask potential users how much they would pay. I would run one survey with open end questions, such as: "which payment method would you prefer? Answers: one time payment, download payment, monthly payments, yearly payments....
and "How much would you be willing to pay for the service - in each of the various payment options".
Then, I'd run another survey with the same questions, but provide various options for them to choose from. There is a lot of psychology behind the way the questions are done, so it is important to do them correctly.
Once you've done these survey's, you'll have a better understanding of what you users are willing to pay, and how. Also, if you do the survey right, you could collect potential first clients (they would leave their email address and you can notify them when you launch).
Good luck,
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