david wolf came very highly recommended to me as well, but he is VERY expensive. was going to charge me about $240 to appraise a 2c stone. i used another recommendation from this board: robert aretz. he was great and substantially cheaper. do a search for his name and you'll find his info.
I'd heard good things about Wolf too but I never got a response to a request submitted via their website. Wonder where that ended up. Didn't Dave Atlas mention Aretz? If so that's a pretty good recommendation.