According to the Unity store page, the $75/month subscription is locked in for 12 months, so it would cost $900 for one year. (click the $75/month price link for subscription details)
If you wanted to update your game after one year, you would need another subscription after that, so maybe $1,800 all up if you plan on updating your game after a year.
Or, you could pay the full one-off $1,500 price and have Unity 5 Pro be yours forever.
Edit: according to the Unity FAQ:
Do I need iOS + Android Pro in order to build to iOS + Android devices?
Unity Personal Edition includes deployment to Android and iOS with the Personal Edition splash screen. To deploy to iOS and Android without the Personal Edition Splash Screen you must purchase Unity Professional Edition together with iOS Pro and/or Android Pro deployment add-ons.
So it sounds like you would also need another $75/month or one-off $1,500 cost for the iOS Pro Add-on on top of Unity Pro.
So all up, you'd have to either pay for subscriptions for one year for both Unity Pro and iOS Pro for a total of $1,800 (assuming you weren't ever going to update your app after one year), or pay $3,000 for both as a one-off.