How can I sign up for a non-free iCloud account (having exceeded the 3 free ones) I have an iPad that has exceeded the 3 free iCloud accounts but I'd like to sign it up for iCloud (and I'd be willing to pay), but how do I do it. 

When I get the prompt that says I have exceeded the 3 free ones there is no option to pay for one.

Signing up on another device may solve my problem but simply stores up problems for the owner of that device as it uses one of their 3 free registrations which is simply storing up issues for them in the future.

Any thoughts greatly appreciated!
Why not just upgrade one of the existing accounts?

http://support.apple.com/kb/PH12796

or see this for deleting unused iCloud accounts

http://www.macworld.co.uk/how-to/mac/how-remove-your-apple-id-completely-shut-down-your-itunes-store-icloud-other-accounts-3474388/

(too much info to précis here, unless votes/comments would suggest it worth it)