Can you tell me what the standard practice is in America and in Israel, respectively, on how to value a kesubah? I.e., how many troy oz. or kilograms are considered the 200 zuzim/zekukim? Thanks.
200 zuz in terms of the weight of silver amounts to very little, perhaps a pound of silver (see Chazon Ish, Even Ha-Ezer 66:21).
200 zekukim, however, can be a significant amount. According to Rav Moshe Feinstein (Iggros Moshe Even Ha-Ezer 4:91-92) this works out to approx. 100 pounds of silver, and this is more or less the ruling given by the Chazon Ish (ibid), according to whom the amount works out to 127 pounds.
According to other opinions, the 200 zekukim are worth far less (such as Rav Chaim Na’aeh, in Shiurei Torah).
The general custom among Ashkenazim (certainly outside Israel, and generally in Israel, too), is the higher amount, which amounts to over $10,000.
Among Sefardim, there are rulings of Rav Ovadyah and others (such as Rav Kapach, who sat on the same Beis Din and issued a joint ruling on the subject), according to which the divorced woman cannot claim more than the lowest estimate.
Note that in general, the kesubah is not relevant, because the wife generally foregoes her claim to the kesubah as part of the husband-wife divorce agreement. However, this is not always the case.