Basically, any Digital SLR camera as long as it has the ability to change lenses. It is the lens that is important in Macro photography, not so much the camera at your chosen price range. However, I would consider a camera at the top end of your stated price range.
Try Canon, Nikon, Olympus Panasonic or Pentax cameras. I personally use the Pentax K-7, because I have numerous lenses from earlier Pentax cameras and, Pentax appear to have the best backward compatibility with its older 35mm film camera lenses.