I never bought my wife an engagement ring. We didn't have much money at the time. I laid out my financial situation for her and asked if she'd rather hold onto the savings that we had or get a ring. She opted to keep the money. I suppose we could get one now, but she's never shown any interest.
On the other hand, for our 16th anniversary, we're going to finish paying off our house and be debt free. That's an anniversary gift that she's excited about.