Well, it gives men a nice excuse: "Honey, let's just live together...I won't marry you until I can afford to buy you the diamond you deserve! It's a matter of principle." ;)
Women have the option to do what I did - choose another stone. When I got engaged, colored stones were substantially cheaper than diamonds. There's nothing "magic" to me about a diamond per se; I have enough that I've inherited, so I didn't "need" one as an engagement stone.