You're forgetting development and marketing costs.

If there is a sunk cost component that number skyrockets.

Try adding a $5 customer acquisition and $1 developer time.

Thats a $1 profit, you need to sell 3 apps to cover the cost of apples fees. You also need to sell another 6 to cover the sunk costs you don't get back.

So 1 refund costs you 9 sales.

To cover the 1/10, you'll need to charge 10.90, or more likely 11 to cover the moving 30%.

But this is just to break even with your original $1 profit margin.