Hydramaster version is cheaper, they sell it in 2 litres kits, (1 litre of each) for £25 last time I bought it.
I find browning with it also, ime this happens with both HMs version and Dye gone. I thoroughly rinse with browning prescription which sorts it.
Somtimes I go 6 mths without using any.
I recently did a job where I used almost a full bottle of Solvex, I thought the same, ooch this has cost me like £15! thats the other pricey one.