The centre stone is only one component
Its origin, carat weight, colour, clarity, cut and documentation affect the quote. A large centre stone may account for much of the cost, but two rings with similar centres can still differ substantially because of their construction.
Metal value is not the finished price
A rough metal-value calculation uses the fine-metal price, fineness and weight. It does not by itself include alloying, manufacture, finishing, setting work or the other costs of a finished ring. Compare the metal and expected finished weight stated by the jeweller.
Construction changes the work
A simple solitaire and a detailed pavé design require different setting and finishing work. Small stones add both material and labour costs. Custom development, matching and the tolerances required by the design also matter.
Compare the same scope
Ask each supplier to separate the stone, metal, manufacture, side stones, documentation and delivery. Confirm whether the quotation covers a loose stone or a finished ring, and which additional charges may apply. Allocate the budget to the features you will actually value when wearing it.
Sources and further reading
This English edition draws on the source material referenced below.