Sump on a Leon is 4.5L and the castrol edge 5W-40 is sold as 4L. I paid £45 for 4L, +£15 for the extra 1L needed, £7 for champion oil filter, so cost me £67 and fitted myself.
They cant be doing it at £28, even if they used cheap oil let alone Castrol Edge, dont garages charge on average about £40 p/h for labour ?