I talked with a fellow today who pays about $200/carat for nice purple or lavender Quahog pearls. For similar, but white clam pearls the price is $50-$90/carat.
These natural pearls are most often sold by weight and other characteristics also count, like shape, condition, color, size.
There are maybe other markets as well, but that is at last one practical price point to consider, if you're thinking about selling your pearl.
Your local jeweler may be able to help you out with finding your pearl's carat weight.
