Quite often, in discussions on this board, we'll talk about Chemspec's Spray N Go or it's generic version of Sodium Metabisulphite. When my colleague was buying some Sodium Met. a couple of years ago, he had prices quoted from specialist chemical suppliers as high as £120 plus for a 25kg bag. In the end he paid about £25inc. V.A.T. and delivery. Chemspec have a list price for Spray N Go refil 0.9kg of £22.61 inc. V.A.T. I've just bought a 25kg bag for £14 inc V.A.T. collected, from a local wholesaler to the "Home Brew" trade. By the time me and a few colleagues have shared it out we'll soon use it all up. I'll do some numbers for you. The same amount as in a Spray N Go tub has cost me 5p.
Safe and happy cleaning:)
Ken