It was $120, so we bought our own GC, and now the local price is close to half that at cannabis labs.
I paid $250 for a full hydrocarbon GC/MS analysis of butane residuals to the PPB level, and $75 each for the PPM tests of the different brands, from a full blown analytical lab.
They have agreed to do cannabis analysis for me, but I haven't heard the price yet, as they still await the required standards.
And usually improves the quality. my excitement at Specialty Analytical entering the cannabis lab arena, is that they have the types of equipment that most cannabis labs can't afford or justify from an ROI standpoint. For instance they have GS, HPLC, and MS.
A GC simply measures retention times, with a known column, under known operating conditions, with a more or less known substance injected into it. Since different substances can have the same retention times, having a general idea of what you are testing is necessary to exclude some.
GC results are handy and have their place, but to really get to the bottom of things, you really need the mass spectrometer, to break the GC peaks down into its composite peaks. That way, you can tell which of the possibilities it actually is, by what it is made up of.