I assume you guys are talking only about bag resellers...what about scarves resellers?sukkar,
Kasumi and Rene are both right. They do charge an arm and a leg here for bags like Birkins, can get a better price for Kellys though. But with the stronger dollar, it won't be as bad in the past. It's also worth it to go to the H boutiques here in Tokyo, if you are lucky, you may be able to find a Birkin (for cheaper than the resellers!)
I personally like going to herpla in the ginza area.
Feel free to PM me if you want more information, although I am certainly not an expert.
There are plenty of resellers around and many of them have loads of H bags in different colors and leathers. You will see many around the Shinjuku area. Hope you find something there.