If you really want to count costs...
Ingredients of pancake mix are plain flour, skimmed milk powder and salt. That's it!
So the only real difference between the packet mix and the Real Thing is that it has milk powder instead of proper milk. Delia's recipe can be made perfectly well with just one egg instead of two (two eggs give a richer batter, but it would still make very good pancakes with one), and without the butter (most of the butter is actually used to cook the pancakes, not to make the batter, and again the pancakes are fine without it), and will still taste better than the packet mix (IMHO!).
So the equivalent of your 15p batter mix would be:
110g plain flour - 3p (£0.45 for 1.5kg)
200ml milk - 9p(£1 for 4 pints/2.25l)
Pinch of salt - cost negligible
(costs based on Asda Price for their cheapest option, could possibly get cheaper from Aldi/Lidl etc)
Total 12p. Flavour and texture of pancakes infinitely better
I love pancakes - lemon and sugar for me too!