The Vilna Gaon derived a slight hint from the Written Torah... The famous verse "an eye for an eye" is actually "ayin tachas ayin" or an "eye under an eye". We do not punish by taking the person's eye if he/she takes out someone's eye; we take the monetary value of that eye. Using the word "under" , the Vilna Gaon points out that in the Hebrew alphabet the letters immediately following (under) the letters of the word ayin (ayin->pay, yud->cuf, nun->samech), can be re-ordered to spell out cesef, or money. Thus the Torah is hinting that money is the retribution for an eye, or whatever the damages are.

Adapted from p. 114 of The Vilna Gaon of the Artscroll History Series