Carly,
My strong recommendation would be to see if you can find yourself: either a second hand Canon 40D or a second hand Canon 5D. Both of these cameras are absolutely fantastic for astrophotography. If you're not interested in using them for standard terrestrial photography -- you can have them modified to pick up the hydrogen alpha wavelength, which is where all the red nebulae hide.
Peter, rebuttal
: whenever someone's handed me a Nikon, I get completely lost -- none of it makes any sense to me! It's all about what you've gotten used to -- so, the ergonomics you mention, mean nothing to someone who's gotten used to using another system. Furthermore, ergonomics don't count for much when it comes to astrophotography as pretty much everything is controlled via software when you tether your system to a computer.
I'm not sure what you mean by hidden features? The three most used things on my camera are modes (aperture/shutter priority, manual), exposure compensation, and focus point selection. Modes are easily switched, exposure compensation is a slide of the thumb on the selection dial/aperture is dialed with the index finger, and the focus selection is done with the thumb on the joystick. All while not even looking at the camera.
Also, Ken Rockwell: lol.
There is a lot, and, I mean, a lot of software support for Canon cameras insofar as astrophotography is concerned.
Have a look on eBay and you will find yourself a 40D or a 5D for $400-$800. The rest of the money can be spent on lenses which will last you a lifetime.
Hope this helps. Feel free to ask if you'd like more information.
H