The actual cost of an engagement ring depends on the materials, like the type of metal or the number and sizes of gemstones. Gold costs more than silver, but platinum is more expensive than gold. Combining different colors of gold bands in a Trinity Ring design, for instance, makes it costlier than a simple white gold band. A small diamond on a Tiffany setting looks so prominent, but an Eternity ring with a paved setting for tiny princess-cut diamonds may cost you more.
Diamonds already have an expensive price tag, but they become more costly because of size, cut, and rarity. The size of a diamond is measured in carats and the skill of the jeweler is seen from the precision of its cut, which lends to its brilliance and symmetry. With a rare stone, like the blood red diamond, the price of the ring goes up.
Believe it or not, diamond rings with silver or white gold bands are more affordable compared to platinum or titanium rings, more so when the gems were rarer than diamonds. These stones include the red emeralds (red beryl) and the fluorescent benitoite, which has a striking blue color and glows under UV light.