This is not how I repair grilles but it's a good DIY method I've used.
Start with 100% pure Acetone, buy a gallon. MEK will work as well but IMO Acetone works fine and is safer to handle, either way wear gloves, either chemical can cause cancer and is easily absorbed through your skin.
Pour an ounce or so into a glass jar (small open mouth jar). Take a scrap grill and using something sharp, scrape off peelings (like pencil shavings size) into the jar of acetone. Put allot of shavings in, the acetone will gradually melt the plastic into a goo. Add enough plastic until the goo reaches toothpaste consistency. Once you have a good batch melted put the lid on the jar tightly and set it aside. Now, prep your grill as normal, V out cracks on both sides, etc. Use clamps near the joint to align the two sides flush and parallel. Smear on some plastic goo, leave it crowned up over the crack like a regular weld looks, let it cure overnight or longer until completely dry and hard. For the strongest welds do not sand the backside or in hidden areas, the added plastic makes the repair much stronger. Sand visible surfaces to flush the next day, or wait a couple days, as before just be sure the material has hardedend completely. Fill any pinholes with Bondo or JB Weld. The crack will practically disappear at this point, paint as normal.
You'll likely find that labor and experience are your biggest "expenses" and that the amount of time you invest will show in the results.
