Cheapest I've found this is on Amazon at £15.99.
Website is rubbish so presume it is just available in store.
All Surface Swingball - Swing ball is a high energy game which will keep you feeling energized. The good idea about this one is that you can take it anywhere to play, as all the components fir easily into the base and then transforms into a sturdy carry case. Just remember when you do set it up you will require either water or sand for the base, the height is adjustable. It comes with 2 bats and is water resistant.