Is there a way to set up some kind of notification for data usage?

I’m currently on an extended stay abroad, and have been using a prepaid SIM card for my iPhone. I generally turn cellular data off whenever I don’t actively need it, but my memory has never been amazing, so I forget now and then; twice in the past four months, this has lead to overuse of data (when my wifi connection failed without my noticing and my data had been accidentally left on), leading to $25 gone in a flash. Is there some setting I’m missing that would notify me when I unintentionally start using data? If not, there needs to be—I can’t help but feel it would be easy to implement, and would save quite a few users money in similar circumstances.