Guinness whistle last week in Belfast international airport: £6.99 in the "Irish" shop (before security check). In the shop after security check £5.50 ;-)

I had to work a bit on the mouthpiece - there were small "wings" of plastic (where the form in which they are cast opens) along the "blade" and along the end of the canal into which you blow
(sorry, I do not know the exact terms for these in English as I am not a native speaker)