You must be joking.

The D300 is the flagship of the Nikon DSLR camera line. I guarantee it’ll be too advanced for your uses. You say you’re new to "these kind of cameras", and as the D300 has much fewer automatic functions and features than en entry-level model such as the D40, D60 or D5000. And, I’m sure you won’t want to spend over $2000 for a brand new D300 kit.
References :

The D300 would be an excellent camera but you made want to save money and go for a D90, the main different is that the D300 has a more rugged built camera body.

If you are looking to move up to even higher quality then you need the bigger sensor and in the Nikon line of camera that would mean getting a Nikon D700 which will cost you about $2400 for the camera body alone.

So either the D300 (or newer D300s), the D90, or the D700. Read up and compare the features, weigh the cost differences and get a good lense for the camera, then invest some serious time learning photography because the camera can be a great tool but only in the hands of those who know how to use it.

Below you should see some web site addresses to some good vendors that can try for prices.

Good luck.

Mark
References :
http://www.bhphotovideo.com
adorama.com
calumetphoto.com