shenfo, you can have the rear bumper bondo'ed and airbrushed. If a pro does it it will look like new after the repair. And bondo on the bumper is not a bad thing; not like filler on the body at least...

Complete job should cost no more than $125-150 at the most.

This is just one company of many that does it. http://carnica.com/paint_repair.shtml