At my local Asda Coryton yesterday were they had 3 shelves of invites, party bags, plates, cups, whistles, hats, bunting etc selling off for cheap.
Waybuloo, In The Night Garden, Disney Cars, Hello Kitty. Most of which were priced around the 15pence bracket. Fab for parties.
This is more than likely store specific...!!! But if you live in the cardiff area maybe worth a look.