Where do you find out how much a gemstone is worth?

Like any other item, it's worth what someone is willing to pay for it.

When you go into the mall and an item is 50% off, divide that number by 5 and that's close to what the store paid for the item.

If you buy a $10,000 engagement ring for your sweetie, pay cash and get divorced a year later, she'll be lucky to get $1000 for it from the same store.

This is a general statement and does not apply to all stores, but I'm trying to show you the vast difference between the wholesale and the retail markets and how difficult it is to say "how much a gemstone is worth". ! :)