I'm an amateur gem faceter -- if you want something that's actually rare, choose a non-diamond colored stone. A ruby or sapphire is far more rare.

Personally, I advocate for lab created stones. It is flawless, you can get the exact color you want (I have something like 20 different colors of sapphire), and won't break the bank. You can spend your money where it counts -- paying for the skills of the cutter -- rather than on a chunk of rough that has been cut sub-optimally to maximize preserving the weight of the stone rather than the brilliance of the cut.