Engagement rings come in two iterations - the surprise and the carefully chosen. You have to consider your ability to afford the ring as well as the ring’s becoming a part of the woman’s (or man’s) lifestyle. Some people have heirlooms that are resized and/or reset from a family’s past as in a grandmother’s ring or a beloved family friend who was a godparent or more than just extended family. These may not be the largest stones or biggest settings but they hold a lot of sentiment and can be added to with other stones, pearls or gold-crafting.
Surprises may be brand new and of the latest style and fashion. They can be by famous designers and can be bought at jewelry franchises in almost any mall or retail area. Prices are determined by the amount of gold in the setting and the number and/or size of the stones or pearls built into it. Generally the bride-to-be does not have input into the selection, design, style or any other factor of the ring unless the groom-to-be has been asking a lot of sly questions or having her family members ask those questions and feeding him the answers. While a diamond is most often chosen for an engagement ring, stones and pearls may be used at the ring-giver’s discretion. Here is where the heirloom might be a huge surprise - several rings, bracelets or necklaces might be combined to make a totally unique ring.
Carefully chosen rings are a joint venture where the couple goes shopping together and try on rings, inquire about prices and stone size as well as setting prices and make a decision based upon their known financial capability and if they want to equally spend for the investment, they can. Some women might choose a sold band with no stones for a wedding ring and not wish to have an engagement ring because of their occupation - sometimes rings are not allowed to be worn - laboratories or nursing/doctoring. I have known women who received diamond earrings as an engagement gift because they are more in step with their lifestyle. Some people choose a modest “first” ring and have it reset and/or added with other stones on significant anniversaries like the 10th or 20th.
Getting engaged can be ring-free as well - taking that money to make a down payment on a house or whatever is not unheard of in some situations.