I found a great offer with Argos.co.uk where you can get a DS black for 79.99 on it's own and the Essentials Kit (RRP £19.99) at £9.99. If you go to the 'special offers' tab below the product description and click on 'special offer 2' it says you can get up to £20 off if you buy the essentials kit and a selected game. I chose Mario Kart DS, however (conveniently) it seems to be out of stock all over the country. But the website doesn't realise this error, and still charges only £9.99 for the essentials kit (that's HALF PRICE!). Then you can take up any other great offer for games from other retailers (such as 3 for £18 at woolworths.co.uk). Happy buying!
Nintendo DS Lite (Black) with half-price Essentials Kit glitch £89.98 @ Argos