You can also repair the grille with a product called Plastex. It is a powder plus liquid activator that bonds and makes high strength repairs on virtually any plastic and fiberglass. [It can also bond dissimilar materials.]
The product comes with a DVD/PC video disk that shows the various repair techniques and methods of applying Plastex.
To repair most of your type of damage, you tape up the repair area in position (I use aluminum tape), and build up the repair using a "dropper" technique, where a small glob of liquid plastic is created by dripping activator into a cup of powder, piercing it with the dropper, and placing it into/onto the repair crack by dispensing a little more activator to release the glob. You can build up voids and create new fully bonded plastic this way. To repair cracked areas that will fit together tighly, you grind a small valley on the hidden side and repair as above. You can gusset repairs with fiberglass cloth too. Missing pieces can be molded using a molding bar they provide, so pieces like tabs that break off can be reconstructed entirely.
The manufacturer is in Nevada, and sells a variety of kits. Powders are black, white and clear. I recommend a "master" kit, about $60 which comes with a little of each powder color, and enough of everything else to learn how to do a lot of different repairs.
I've repaired door panels (like the rear seat courtesy light grills that melt from the bulb), console parts, built an A pillar gauge pod, and many other plastic projects with this product.
