[Digestion] Biogas concentration sensors - technical question

[Terrence Sauvé]

Hi all AD enthousiasts,
I am currently preparing for my thesis on AD and co-digestion for medium size dairy farms in Ontario, Canada.
I am having difficulty finding a "decently" priced biogas sensor to measure in-line concentrations of methane, carbon dioxyde and hydrogen sulfide for both lab-scale and full scale applications. 
There is a few companies in Germany that offer that service but for around 7'500 to 10'000 euros price range.
Considering that we also have to run VFA's, based on those prices, we might as well buy ourselves a GC and a bunch of columns with it.
We were also falsly recommended by a company to purchase a hand-held portable gas detector, commonly used in the natural gas security industry. However, these sensors are catalytic and only works at normal atmospheric pressure...

I would like to receive your feedback on this issue and if you have any technical experience with brand-name IR adsorption of "in-line" gas meters.
Thanks all.

Terrence