Infocus X1 (link goes to review) is supposed to be the hot shit for value. It is a little more than you indicated - I just saw one on ebay for $860. As far as aspect ratio goes, that is the cool thing about projectors - they show them all, not to mention at large sizes. You'll be displaying 4:3, 16:9, and everything else. Screens are good because they are reflective, which the paint on your wall isn't. This will allow you to run the projector at a lower contrast and brightness, extending the life of the bulb (which can be a factor). You'll get a better picture on a screen. For really detailed info, you might check out
the avs forum. The guys there have some high-speed info on projectors. In general, you won't be happy with a projector unless you have serious control over the light in your viewing space. Good luck!