$100 or thereabouts. I don't believe Tenax is double-butted, tho. In a question posed by Stan Cooper about exactly what kind of tubing Tenax was, Richard Schwinn responded:

We don't have the detailed answer. It was a lower grade of Columbus tubing - likely a non-seamless (welded/re-drawn) non-double-butted chromoly. That would make it affordable on the $5-800 Schwinns built at the Mississippi factory.