Sainsburys Chesham (don't know if it's national) are selling tubs of 50 red, blue and black ballpoint pens for 99p. Reduced from £4.99. 2p a pen. They are also selling tubs of 30 gel pens down from £6.99 to 99p.
£1.49 from Sainsbury Online if you don't mind the 50p extra.