I'm unaware of anything offered by Sky which costs �5 per month. All of their 'packages' cost more than a fiver.
A Sky box without a valid card in it can receive the unencrypted ('Free to air') channels from the BBC, ITV and a few other broadcasters. This can be upgraded to receive the encrypted ('Free to view') channels from many more stations (which are collectively known as 'FreeSat') for a one-off payment of �20 (which provides a valid card for these services).
I advise that your friend should contact Sky, as soon as possible, to find out what he's being charged for.
Chris