EE has never claimed to be the cheapest network, and a figure of £5/month is something I'd not be surprised of from budget and/or MVNO providers.
Those budget providers may not always have the same service levels or facilities as the main networks - also be sure which network hosts an MVNO, and check their coverage & service levels in all the areas you frequent and use your phone. Online coverage maps are only a prediction and don't predict mobile data service.
