I think there's something about a pretty, in good taste ring that's highly sentimental not only from cultural perspective, but also personal one. It doesn't have to be something expensive, but something reflective of both partner's personalities, aesthetics and emotions. Something about her wearing an ornament that came from you that's very indicative of the future. This shouldn't be subject to amount of money spent on it though.
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~