This seems to be the cheapest I can see for the DS lite console, using the voucher code below. It is £100 online, but you would get it for £80 (including the 20% off) + £3.50 shipping. It is also available in white from this site for an extra quid! The only problem is the 3 week delivery from the supplier, but that would fly in!! There is also the possibility of getting 6% quidco (about a fiver cashback).
Promo Code: D5JW
Thanks to biggerfella in the deal requests forum!
Details: New Nintendo DS Lite - It's 60 Grams lighter, 30% smaller than the original and features a new brighter backlit screen