Is there anyway to restrict iPhone data use?

I have an iPhone 5, and as my family don't have any ADSL Internet (Telstra refuse to put in the needed cabling for the foreseeable future) we don't have much in the way of Internet. I get 700mb of Internet, although I manage to go over every month from browsing (average site is around half an mb, visit around 100 sites a day)

Is there any app I can get that will set me out an allowance of data for the day and then cut off or alert me when I reach the limit? I don't want to keep running over my limit, it's running down my parents and I can't afford to pay the rates

You can access the usage menu by the settings app > general > usage > mobile data, and that will tell you how much you use (you will have to reset it monthly though), try turning off all unneeded services like icloud, push emails, photo stream. You can also restrict the sites you visit by using eg a mobile version of the site if it's an option, if you use a maps program then don't use sat view as this uses more data, hope this helps