Hello,
I am looking into building/obtaining a modest GC/MS (Gas
Chromatography/Mass Spectrometry) system for avocational use. I am
aware that used devices are available from Internet auction sites for
around $500.00, but I am also aware that there are significant
accessory requirements for their use, such as carrier gas systems.

I am interested in knowing about how much I should expect to spend to
build a working GC/MS system of basic functionality and calibration.

I am interested in knowing what the major components and accessories
in a system (besides the box) would be, and their general costs.
Examples might include carrier gas supplies, tank rental, and gas
plumbing to the tank.

I am also interested in knowing where there are major differences in
vendor-specific consumables pricing, and if so, which vendors might be
more affordable for a low-volume hobbyist user.

If field-of-use is at all helpful, this would probably be used mostly
for personal research into flavors and fragrances. I also have an
avocational interest in toxicology and could see myself using it for
assays of common household materials and/or water samples.

My guess is you can cobble together free junk on trash day and stuff
from junk yards for less than $50 with good luck and lots of know how.
Perhaps you can get several owners manuals for similar equipment from
Ebay or an owner will let you copy the important parts of his
instruction manual. You likely need calibration instuctions to get
most professionals to accept the calibration job which may cost over
$100 if you need certification of accuracy, but that could easily be a
problem with a used machine which does not have an adequit instruction
book. As I said I am guessing.  Neil