Cheapest I could find anywhere. This is £9 on amazon.
Seems like a good deal
Get your message out with style, but keep your secrets with Nerf Rebelle Messenger Blaster. Your performance will be top-notch when you launch your Message Darts at targets up to 75 feet away. But you can also make your mark as a spy, because each dart contains a secret message that can only be decoded with the included decoder. The special pen hidden in the handle writes hidden messages on the dart and once the message is delivered, you can erase the message and write another. Give the decoder to a friend so you can send coded messages in plain sight of your opponents. Show your spy style with the Messenger blaster. Nerf and all related characters are trademarks of Hasbro.
** Instore deal - See link for product info only