I'm not aware of cheaper assays that may have been developed. So, yeah, it'd likely require buying a GC-MS (>$50,000), plus a gas source, whatever MS software, and some training.
Alternatively, for ~$50 there are many core facilities at universities and elsewhere that'll happily run whatever sample you send them and email you back the results.
Alternatively, for ~$50 there are many core facilities at universities and elsewhere that'll happily run whatever sample you send them and email you back the results.