Though Mr. Kassam does design jewelry that costs $100,000-plus and works with Hollywood celebrities, he more often designs rings in the $10,000-$50,000 range.

“Everyone is on a budget,” said Mr. Kassam. “Everyone is looking for value at their price point, even if that number seems high to someone else.”

Other custom jewelers work in similar ways. Briony Raymond meets with couples at her atelier in Manhattan to discuss styles, materials and budgets for an engagement ring. Those budgets, she says, can range from $3,500 to hundreds of thousands; on average, rings are $30,000. No matter the price points, she really tries to nail what the proposer envisions for the ring, whether it’s something designed from scratch or utilizing parts of an heirloom ring. She often includes diamonds or other gemstones from family pieces into the ring, an element that makes custom a truly rewarding experience for the couple. “Finding ways to blend two family cultures into a creation speaks to the couple and pays homage to their pasts,” Ms. Raymond said.

“There is no question that one gets far more value in the end when we are working closely with them and championing their vision.”

Several traditional and online retailers have jumped on the bandwagon with semi-custom online products that help consumers craft a ring. Ritani launched their “Design Your Own Ring” feature online in 2012, allowing consumers to build a ring. The ring configurator showcases thousands of settings, filtered by style, metal, price and delivery time. It offers more than 75,000 different stones. Josh Marion, vice president of Ritani, explained that the buyer can refine their search beyond the four C’s, looking at advanced options like polish grade, symmetry and fluorescence, which often have greater impact on the final appearance and value.

Other popular online retailers, including Zales and Blue Nile, also offer digital tools. Zales claims more than 14 million available combinations from their 12 ways to customize on their site. Blue Nile’s customization process can be completed in mere minutes, and there’s even overnight shipping. Katie Zimmerman, the chief merchandising officer at Blue Nile, explained that the majority of their customers use the feature when purchasing, and their ready-to-ship rings are actually preset options based on the most popular combinations from their build-your-own-ring tool.