Being fortunate enough to use all of them -- D200, D2Xs, D300 and D3, I can say that there are a lot of good reasons to go right for the D300, but there are also a lot of good reasons to pick up a used D2X/s somewhere. I doubt that you'd find any for less than $2000, though -- don't know where you got that figure of $1200.00. I suspect you may be seriously and quickly disillusioned if you think you can pick a D2X/s up that cheaply....
The D300 feels a lot like my D200 -- but oh, so much better and faster! Without the grip it's a bit lighter and smaller, which can be handy at times. With the grip it is close in weight to the D2X/s and the D3. While some of the features and functions of the D300 now seem to be on a parallel with or even exceed the D2X/s, there is still a distinct difference in the body and build. Once you get accustomed to handling a pro body, other cameras just do not feel the same. The D3 and the D2Xs feel more similar to each other than the D300 and the D2Xs, regardless of specific new features and functions.
One great thing about the D300 is that it will use the EN-EL4a batteries in the grip, which then increases the fps that you can shoot -- a valuable asset in shooting sports or any sort of action. You would need to buy the optional battery chamber, an EN-EL4a battery and charger in order to utilize this. On the other hand you can still do pretty fast shooting with two EN-EL 3 batteries, too......
Even though I have the D300 and the D3 I am still going to hang on to my D2Xs for a while, as there are definitely features of this camera which fall in between the D3 and the D300, and it's still a darned good photographic tool. Some have mentioned that they still prefer the color in the D2X/s to the D3 or the D300; I haven't decided about that one way or another.
Probably the thing to do is to assess what you're really looking for and what you really need in a camera. If it's high speed, the ability to reach higher ISO without noise (or with very little noise), if it's a larger LCD screen.....then go with the new D300. If you really aren't planning to shoot at high ISO, if you aren't intending to use this for high-speed action photography (sports, wildlife, birding), go with the D2X/s. You mention shooting sports and action during the school year; for that the D300 probably would be your better bet, especially if you need to reach high ISO at times at night games or in dingy gyms. The 51-point AF system is amazing and definitely is excellent for shooting sports.
Why not go to a local camera shop and handle both cameras, see which feels best in your hands? Look at DPreview and other photography sites online and read comparisons between the D300 and the D200, the D300 and the D2X/s....
Good luck with your decision!