You could always use a webcam and stack the images to increase exposure, works decently well for the larger planets. Or with a good tripod you can get star trails, but if you really want to get into astrophotography you really should get a decent telescope with a equitorial mount, preferably motorized as well as a camera mount for your camera. High MP does not matter in this situation, a 3 MP camera will work just fine. Otherwise for higher MP cameras, the ability to bin photosites is invaluable.