I have performed ASME code welding of boiler tubes with a bobcat. It works fine for most tig applications using DCSP.
You would need as a minimum a Bottle of Argon, an air cooled GTAW lead and torch (A weldcraft WP9, 17 or equivelent), a flow meter, and tungsten/tig torch parts. A power adapter is also required but is sometimes supplied with the power cable.
I have a 20 CuFt Bottle(I suggest one bigger) and the above setup and have less that $160.00 in it which includes the shipping I had to pay.
I have seen pretty good prices on tig rigs (Cable and torch) on e-bay.
Have a nice day
G Austin
http://www.weldinginspectionsvcs.com