I keyed in completed listings on ebay for Tahitian pendants, below. Very roughly, it looks like they've mostly sold for between $100 and $200. But only the ones with the price listed in green sold. The red prices didn't sell, and most of them are in red. The price might be higher if the diamonds are real, if the gold is 18k, because a chain is included, if you have a receipt or other paperwork with it, if the pearl is exceptionally beautiful, and with larger pearl size (9mm is small for a Tahitian)...
Many people seem to decide to keep their jewelry for someone special after they see how little they're likely to get for it. Most jewelry just doesn't have great resale value. Also, just my opinion, but I wouldn't sell the earrings with the pendant, if that's what you had in mind. I guess "fake" is just not a word I want in the vicinity of a real pearl I'm considering buying from ebay. Good luck with it.
http://www.ebay.com/sch/Pearl-/1643...w=tahitian+pearl+pendant&_pgn=2&_skc=50&rt=nc