These were reduced to £17.00 in asda Wolstanton today, the lady who served me said they were only reduced today.
It's locked to Vodafone but unlock codes are only a couple of quid.
Will do nice as a spare phone at that price, got it all set up and it's updated to marshmallow so you can use the sd storage feature if you want more than the 8gb internal.
Unsure if nationwide but the price was on a printed shelf edge label.
EDIT: forgot to mention no top up was needed either.