Rashi: A person uses one limb to save another. If a knife approaches his head, he protects with his arm, and all the more so he will give money to save a limb. He will give everything to save his life. Iyov knows that he is Chayav Misah, so he is not pained that he redeemed his life via loss of his money!

Ibn Ezra: Normally, if one fears lest his eye be stricken, he puts his hand over it, for the eye is [more] esteemed.

Devar Eliyahu: Man is primarily composed of skin, flesh and bones. Sinews are merely to connect the bones. If You will strike Iyov's flesh and bones [he will curse You]. The first losses were not a test, for if a vital organ is about to be stricken, one protects with his hand, even though his hand will be stricken. All the more so one will give anything to save his life!

Malbim: The previous test did not show that he serves amidst love. One's body is dearer than his money. Perhaps he serves amidst fear, lest his body be stricken! Man has two skins - his own, and Kusnos Ohr (clothes from animal hide). He would forfeit his clothes to save his own skin, and give anything, even his own skin to be flayed from him, to save his life. Even taking his own skin is not a proof, and all the more so his external skin (property and clothing)!