How much data does an iphone 5 use each month?

I currently have a blackberry q5 and I receive 1000mb / 1gb of data per month as part of my contact, but I hate my phone, and as I have another year left of my contract I thought I'd buy a cheap second hand iphone 5 of hunters or something, and but my SIM into it so it would be the same contract, but I wondered if 1 gb of data per month would be enough because I hear that iPhones use up a lot of data

It does use a lot of data IF, you leave your data enabled all the time and have lot's of apps that uses data in the background. However, 1 GB is actually quite a lot, so unless you are going to use the internet heavily, it should be enough. But as said, you could always disable data and even use Wi-Fi to avoid using your data.

Yes, we're data hogs. IPhone users suck up more data like a Hummer than anybody else.
http://www.analysysmason.com/About-Us/News/Insight/iPhone-data-traffic-Jun2012/

http://www.androidauthority.com/iphone-owners-use-more-data-129207/
But a 1gb plan can work provided you track your usage with the phone's counter and have access to Wi-Fi somewhere. For general use 1gb can get the job done. You won't be streaming movies or playing a lot of games but you can do everything else. Best luck.

It uses as much as you use, iPhones use no more data than another smartphone.

Your foolish if you think there are cheap iPhone 5s available, a used $650 smartphone still holds its value for years.

It depends on what you do & how much you do it.