Average data transfer size when playing?

[Calrive]

I'm playing Pocket Legends on a 3G connection which has a 100mb monthly allowance as part of my post-paid plan. Can someone please advise me on average, how much data would transfer on my phone connection with 30 minutes of playtime?

I don't want to exceed the 100mb because the excess charges are pretty expensive (yea I got a crap plan =[.) Thanks.