Dual Band Wifi Dongle. Amazon.
Claims to be reduced from £26, but I've seen it retailing more realistically around the £18 mark.
Steal at this price, if you have prime. Can't see it cheaper anywhere else (if you're going to make the claim, at least post the link to benefit others).
Read reviews etc, posting this deal because I bought one myself.
I'm sure somebody will say they've owned one, and it died "after a day" or something. There are 671 reviews averaging at 4.5 stars, which is why I'm taking the gamble. ;)
EDIT: This is NEW not 2nd hand like the previous deal.