I found the 5 reagent method and it uses a spectrophotometer
"quoted in Aubrey Knowles' "Colorimetric Analysis of Metal Finishing & Metal Working Solutions & Effluents" (1999) with sensitivity given in the range of 5-60 and 1-20 ppb, respectively, though I suspect that for the lower end of the range you'll need to use a cell with a long light pathlength (e.g. 10 cm)- check to see if your HACH can accomodate such cells. Essentially, both methods involve oxidation of HCN to cyanogen chloride which is then reacted with methylphenylpyrazolone, bispyrazolone and pyridine in the first case, barbituric acid and pyridine in the second case. Both complexes absorb in the visible (580 and 620 nm resp.) so any working spectrophotometer should do for the higher part of the specified concentration ranges.
Note though that if part of the cyanide is present as metal complexes (which is likely) then a decomposition-distillation-absorption procedure becomes necessary for the separation of cyanide, and it is very tedious. "
I guess the later is why it costs about 3K for a test
Steve
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