Your Xbox doesn't run anything at 1080p. It may upconvert stuff from 480p, 540p, or 720p, but there is very little, if any, native 1080p on the Xbox. Your finances are your business, so that's a legitimate concern, but your statements about relative quality are somewhat misinformed.
edit: Didn't you have to buy a replacement 360? Where is that cost factored in?

