How much mobile data does Pokémon Go use?

How much of my monthly mobile data is being used up by Pokémon Go? Pokémon Go is a really fun game, and part of what makes it so interesting is the fact that you need to go outside and move around to play it effectively. That of course means you'll be out of the range of your home Wi-Fi network, using up mobile data as you walk around. Some "tricks" like downloading offline maps in Google Maps won't actually save you any data usage (though it's a great feature for Maps!), and unfortunately the...