Well I found this one on Amazon. Has really good reviews..And it's only 56 dollars...So I'm tempted to buy it. Hmmm..
Amazon.com: Zeikos ZE-NBG300 Battery Power Grip for Nikon D300 & D700: Electronics
I have both the Zeikos and the Nikon grips.
The Nikon grip has the same magnesium-alloy body the camera has. The Zeikos grip is all plastic and makes other compromises in materials to keep the cost down.
The Zeikos grip looks and feels pretty much just like the Nikon grip. The controls on the Zeikos grip don't feel any different than the controls on the Nikon grip.
So far, the Zeikos grip is performing just as well as the Nikon grip.
My only reservation with the Zeikos grip is the plastic body. I keep a quick release plate mounted on the bottom of the grip and I use the plate's D-ring to hook a Black Rapid sling to the camera/grip/lens. If the plastic grip body fails at the tripod mount where the quick release plate is mounted, nothing would be holding the camera/grip/lens to the BR sling.
As far as vertical grips in general, wonder why the pro level Canon and Nikon cameras have one built-in.