I guess charging a fee for none Talktalk customers is better than just closing the accounts, but £5 PM does seem a lot for just an email address. Especially when there are several free webmail services available.
If your privacy conscious and worried about having a Gmail, Yahoo, Hotmail etc then as others have mentioned, you can buy a domain name and setting up your own email and you have full control over it and it would be cheaper than even the £50 annual fee with Talktalk.