on ebay that is below retail ??? - Authentic of course
Possible? Yes. Risky? Most definitely!! I personally would save my pennies and buy one from a reputable retailer like Saks. It hurts the wallet, but at least you know it's real.
An authentic Stam (even used) goes for more than $1k on ebay; ebayer Personalshoppers (trustworthy) recently listed several Fall '06 Stams for a little less than $1200.
Stam is MJ's most popular bag since debuting in Fall '05, it has the best resell value. The most-in-demand Stams are the discontinued colors and/or those with suede linings.
I don't think an authentic Stam will go for less than $1k. I second the recommendation of Personalshoppers. I bought an authentic Chanel from her-wonderful service.