a diamond takes so long to make, and they are very rare esp. those over a full ct. in weight. The size is not the only factor for their price, they are also graded on color, clarity, cut and so on. A diamond that is flawless is quite rare, and EXPENSIVE. If you are just looking for a ring with a diamond of impressive size, go to a used jewelry dealer and just have the stone reset in a new band. High-end stores often jack the prices way up, if you tried to sell back the same ring to someone else they would give you maybe 1\4 of the price you paid if you are lucky. Because of this it only makes sense to buy used.