...actually, as an aside, it's always worth checking what the active ingredients are in various branded formulas, as it's quite easy to find cheaper alternatives....
We're about to try a little project that needs some muriatic acid, and copper sulphate.
Muriatic acid is just diluted hydrochloric acid, and turns out, that's exactly what brick and concrete cleaner is - so £7 for 5 litres is a lot cheaper and more readily available than buying stuff from chemical suppliers.
Copper Sulphate - turns out it's widely used as the active ingredient in 'root killer' for gardeners, but because it's branded as such, it's got quite a markup on it. A bit of hunting around, and it turns out that Copper Sulphate Pentahydrate (which is how it is almost always made up at regular room temperature - it's just hydrated Copper Sulphate crystals) is used by farmers to dip sheep's feet to prevent various fungal rot etc. The local farm supply shop sells Copper Sulphate crystals in this form at just £7 for a kilo tub.
So £14 in total - about half the price of buying stuff without digging around a bit.