Workstead, A high frequency unit changes the characteristics of the weld current to make it easier to start & maintain the arc. TIG is a high precision, clean, flexible process that's not difficult to learn but takes a little more equipment. TIG will do everything the homeowner wire feeds are bought for but won't do, and a lot more.
280289262424 is an example of an EBAY item availible. They come and go. Search for "frequency" and Lincoln,Miller, Century, etc.
http://www.stanford.edu/group/prl/documents/html/TIGweld.htm is a TIG primer.
www.millerwelds.com/om/o610g_mil.pdf is a typical HF unit owners manual.
I talked to a guy Saturday that took 1700 lbs of scrap in last week and didn't get enough to cover his fuel for the trip. MikeD74T