In my experience the only weekend of the year to get a discount in the UK is AeroExpo. All the usual suspects have stands there and always have show specials on Bose and Lightspeed. Visit the different stands and then play them off against each other.
UK customs might catch you coming back from the USA, then your saving will turn into an increase. They know how valuable these things are and buying one will inevitably put you over your allowance.