Another company that does sell higher carat diamond engagement rings is Tiffany. Tiffany, the luxury jewelry company, sells premade and custom options. You can expect to spend an eye-watering $257K on a 5-carat diamond engagement ring from Tiffany, on average. Tiffany has beautiful designs, but it’s not the best option if you’re looking to save any money on a 5-carat diamond ring.