Lidl will have these waterproof massage cushions instore from Monday 03/02/14 for £7.99 which seems pretty good, they come with a 3 year waranty as well.
Product Information :-
Enhances your bathing experience with soothing vibration message for neck and shoulder area
Waterproof and with two suction cups for easily affixing to bath
With a removable plush cover
3 year manufacturer's warranty