Hilchos Ishus 10:8

The dinar of the kesubah need not be of pure silver; the coin of the time was made of seven parts copper and one part silver. A sela (i.e., four dinar) contained a half-zuz of silver with the result that the 200 dinar of a virgin’s kesubah equaled 25 zuz of silver and the 100 dinar of other women’s kesubah equaled 12.5 zuz of silver. As has been discussed elsewhere, a zuz is the weight of 96 barleycorns; a dinar is called a zuz regardless of whether it was of silver or of the mixed metal of the time.

Hilchos Ishus 10:9

A virgin’s kesubah may not be less than 200 zuz and another woman’s kesubah may not be less than 100 zuz. If one writes a kesubah for less, the marital relations are considered a licentious act. Marital relations are permitted whether the husband has written the kesubah in a document or whether he has witnesses observe him making the appropriate financial commitment to his bride and perform a kinyan (act of acquisition). Similarly, if he gives her property equal to the value of the kesubah, he may engage in marital relations with her before the document is drafted.