Waitrose is selling its Christmas cake kit at the moment at 1/3rd off (£6.66 instead of £9.99). I reckoned that it would cost that much if I purchased all the ingredients separately (and ended up with a load of unused, dried up raisins etc.)
Although the kit is supposed to be for a 7" tin, I've found that there is enough for a 6" cake for us and a 5" cake to give to MIL.
Both cakes are now slowly cooking in the oven and the kitchen smells lovely and spicy.