Cheapest i have seen is £300 @ eBuyer!
To get for this price:
1) Visit Logitech's trade in program here: http://www.logitech.com/en-gb/349/7016?WT.ac=ps|7041
*You don't actually have to trade anything in*
2) Click on the "Trade in your old product" link
3) Fill in the details (Does not have to be accurate, No need for a valid email)
4) At the end you will be given a 20% off discount code, use this at the checkout to get the deal price
Following on from the company's high-end Z-5000 range, the Z906's THX-Certified audio capabilities deliver 500 watts (RMS) worth of punch, and claim to deliver a theatre-quality sound experience.
Digital Detail: Onboard 5.1 digital decoding enables detailed surround sound-from the roar of the crowd to the footsteps right behind you-in your Dolby® Digital or DTS® encoded soundtracks.
Quality Control: These speakers have met strict performance standards to achieve THX® certification-so you can be sure that your entertainment will sound the way it was meant to.
Immerse Yourself: Make any night opening night. 500 watts (RMS) of power delivers thunderous audio that can shake your house-and your whole neighborhood.
More Flexibility: You can connect up to six audio devices simultaneously, including your TV, DVD, DVR, Xbox 360®, PLAYSTATION®3, Wii™, iPod and more.
Fits Right In: With its easy-to-read display and easy-to-stack design, the control console will look good in your home-entertainment setup.