Once you get a new copy, install the disc immediately. This stops the disc from spinning while in play, thus lowering the chances of scratch. As suggested by Mind M@ster, never set up the 360 vertically.
I've had the same experience with my L4U disc, except I had it set up horizontally and a little brother of a friend's bumped into it...
Good luck saving up for it. Surely by the time you get the money, it'll decrease in price.