dSLR or External Display/MIDI keyboard

I have decided to spend a little bit of money coming up and was wondering what I should do. I was thinking about getting a Nikon d3000 for $500 at the camera company (with kit lense). Another option I was thinking was getting a keyboard to use with garageband and an external display for my Macbook Pro (HP or Acer most likely) In my situation what would you do? I could put away the couple hundred dollars I would save by going with the second option, but I would like to get into photography. If I do choose to go with an external display what size should I get? Is 18.5 in. big enough. I'm looking for less than $200 on the display though.