Kiddushin 11 - How Much Money is Needed for Kiddushin?

Beit Shammai required for Kiddushin a minimum of a dinar, a coin with silver content equivalent to 96 grains of barley. What is their reason?

Self-esteem? - No, because then some would require more.

Is it because when Torah mentions Kesef (money), it means a silver coin? This withstands questioning.

Or is it because we compare a bride to a Jewish maidservant, who is redeemed by diminishing the price for years served, so she needs to start out with a dinar? This also withstands questioning.

The law follows Beit Hillel who require only a minimal coin (prutah, about 5 cents).