How much does a single black pearl cost?

I want to ask a jeweler to make a necklace for my wife with 3 black pearls on it. It looks something like this: http://www.bluenile.com/freshwater-pearl-necklace_3849 (but from white gold rather than silver and with black pearls rather than white pearls). The jeweler gave me a quote of ~$300. How do I know if the price is fair? It would be great if anyone could answer quickly since her birthday is coming up and as usual I waited for the last minute...Thanks in advance. Tom.