I have just been to Asda today and got a pack of 3 pairs of mix and match pyjamas (ie tops and bottoms) for £5 - they only up to age 2 unfortunately, but still a good deal as packs of two pairs are usually about £10-15! They have got some nice bright designs amongst the sea of baby blue and pink, too.
HTH someone I'd say definitely worth it even if your baby is much younger and still in sleepuits, just get a pack of the larger size.