it is possible to decide how much a ketuba is worth from the fact that the Torah says one homer of land is redeemed by fifty shekels. One homer is thirty seah and one seah is fifty by fifty square cubits. So a homer is 750,000 square cubits of land. That comes to about one and a half acres. So that is the ketubah of the Torah which is also fifty shekels------------------however, the obvious question on this is that the evaluation of the Torah and the monetary value of a field are two different things.