If you can find out if she likes diamonds, in and of themselves, I really like what my husband did -- he proposed with the diamond, like literally a diamond all by itself, and then I designed the ring that would be the setting for it.
I never had any preconceived ideas about how much my husband should spend on a ring...I think that's a highly personal decision! I know people with a lot of money who chose simple gold bands, and others with a very modest income who took out loans to buy the spectacular ring of their dreams. Don't let the jewelry industry fool you into thinking that "everyone" spends a certain amount.
I love having some family jewelry from both sides. But those rings were chosen to symbolize somebody else's commitment. It is not the same as picking out a new ring with my partner to symbolize our new life together. I wanted a ring with no history except ours.
I think if someone is going to wear a ring every day for the rest of their life, they should be able to choose what they want. I insisted that my husband choose his own ring, too. His style doesn't match mine, but that doesn't matter to us. We both got exactly what we wanted.
Before my hubby proposed, every once in a while when we walked by a jewelry store he would say something like "wow, look at the size of that diamond, could you picture yourself wearing something like that". That's how he knew what size I would like. I don't like big gaudy rings...small and simple is what I wanted. Other than that, he did everything else on his own, and I love the fact that he did. He went to a few jewelers and asked questions and some of them gave him a tutorial on how to pick out a good diamond. He ended up taking his mother with him and he said It was a great experience. His mother was thrilled to help but he really made all the final decisions. I wouldn't want to pick out my own ring because I love the tradition of the whole thing. It means so much to me that he picked out something with my personality in mind. It wouldn't be the same if I helped. Oh, and he spent 2 months salary on it. I wouldn't have let him spend that much but he really wanted to.
I don't like the idea of engagement rings personally... or weddings for that matter. I think that at a time when you're just getting ready to move out together and get a bit of a start in the world, sinking much of your money into these things is foolish. Plus I don't think romance needs physical signs and symbols.
But I know most people feel differently about the issue than I do.