trading skins

I've been reading Henry Morris' commentary on the book of Job.  Of course, the culture and traditions jump out at me.  Here's one to share with you...
Satan knew Job was the most godly man on earth. Satan had allowed (Noah) to escape his control...Before that he had been permitted to test Adam and Eve and he was successful with them.  Here he was again, knocking on God's door for permission to pester and try Job.
Satan requested a second even harder test for Job, the first being to take from him everything he had.  Now he planned to attack his flesh.  He said to God:
"Skin for skin, all that a man has he will give for his life."  Job 2:4
I've heard the phrase skin for skin before, but didn't know what it meant. 
In those times, men often used animal skins they had for bartering.  They would trade a skin they had for one of equal value and from a different type of animal.  I can imagine a line of camels traveling to and from market, over the desert path, piled high with supple, colorful animal skins.  Perhaps traded  for other goods...live animals, spices, salt, precious minerals, etc.
Here, Satan is suggesting Job give up his very skin in trade for his life (I think).
This saying is unfamiliar to me, but it sure gives my imagination a 'kick-start'.
Here's one way to use animal skins....