To return to the original question, and speaking as yet another accountant, I reckon on roughly £1 a litre. I try to do actual sums in SI units, because SI units work much better than Imperial units for boring stuff like science and because I brew to 25L which might get you 48x 500ml or thereabouts and that is either 12x 2L in old cider bottles or 2x24x 500ml Coopers bottles. Each stores quite neatly.
So one batch might break down as £8 for grain, £5 for hops, £2 for yeast, £6 towards a replacement for ever more frustrating Grainfather that cuts out at 70-odd degrees C and the £4 for the "rest" represents the other kit I accumulate slowly but surely and stuff like water, chemicals to add / clean and electricity, which sure as hell ain't free.
Most of the "costings" people do (to tell SWMBO?) tend only include proximate ingredients like, say, the can and the sugar, at its simplest.
A brewday for me takes ~6 hours. Playing around with it - milling grain (and better still, roasting it in oven and stirring every 20 mins,
) racking / bottling and generally moving it around could equate to a total of a full working day per 25L brew.
We might compare it to other middle-aged-bloke-type-pass-times like golf. If you were to work out a cost per hole of golf, maybe it comes out similar to a litre of HB? (Here comes the sums: 70 rounds in a year at 18 holes a year comes to 1,260. Does £1,260 cover membership, the hardware, disposables and travel costs?)