Nintendo games tend to hold their value for months if not years, but we've seen some seriously decent deals for Donkey Kong Country Returns 3D lately.
But none as cheap as this. HUKD member r simsini has found a copy for just £3.00 in his local Sainsbury's with the receipt to prove it, so it might behoove you to get your skates on and see if your nearest store are running the same ridiculous offer. It's totally... bananas... I'm so sorry everyone.
If you can't find a copy, be aware that Donkey Kong Country Returns 3D is now just £19.95 on 3DS if you order online using Rakuten voucher code MARGIFT5.