Forget any kind of touch-up, you'll need to get the whole bumper repainted.
You can clean up & sand the deep scratches to prep them for bondo and more sanding/smoothing. Matching a paint color is very difficult and getting a *good* finish out of a spray can is pretty unlikely.
Do the body filler and sanding work yourself and then take the car to a "mr. bumper" type place to get the bumper repainted & clear coated. ($160) A regular body shop will probably remove the bumper for painting which will push the cost to $300 +. If you have an air compressor and a decent spray gun, NAPA can mix up a quart of factory paint color.
I recently had my front bumper repainted after filling in some major gashes/chips and it came out pretty nice.
