Gander Mountain is high. I paid $545 for my P99 3 months ago. The gun is really sweet in 9mm. In 40, it will have a lot more muzzle flip. I think U will be happier with it in 9mm, as it has a high bore axis.
Gander Mountain will also not deal, unless the weapon is scratched. I looked at a p99 at the Houston Gander Mountain a few months back - I even told them that their price is ridiculous. They are pretty much AT LEAST $50 too expensive on all of their handguns, if not more. They have a nice seletcion and I like to look there. But, that's all.
U will want the A/S model - it is what the P99 is famous for. The QA trigger is similiar to a Glock - the same on every shot. But, it is too heavy. The A/S is rare, but they are being imported again since Spring of 2006. And, U may need to have a local shop order U one. But, they are out there.
Anything over $600 is a rip on a P99.
As for the exact model # - go to the Walther Forum ( www.waltherforum.com ). I've seen people there who know the exact sku #'s of the gun and what is what.