Most of the newer drives are less than 8", for example the Samgsung SH-S182D happens to be on newegg's front page, a trip to the manufacturer support page has a link to the product manual and it says "Size(Width x Height x Length) 5.34 X 1.65 X 7.24 Inch (148.2 X 42 X 184mm) ", looks like you are in business for only $30 including shipping!
The shortest ones out there I'm aware of (besides slim laptop ones) are the HP and Lite-On ones. I have the HP DVD740i (i = internal), and it's ~170 mm long. These two brands are essentially the same. Both offer DL drives supporting that image-burning technology so you can burn a picture right on the top of your disk.