The replacement grill/griddle is sold separately and is a lot cheaper than a baking steel.
I have cooked pizza on the grill even before we got the grill/griddle. It's too hot here in the summer to be futzing around with a very hot oven inside running against the A/C.
Everyone says you can throw the raw dough right on the grill for a few minutes until in stiffens up, flip onto a platter, quickly place your (not too heavy) toppings on the cooked side of the dough return the pizza to the grill, and close the lid to finish the pizza. I'm sure this can be done, but I haven't tried it. I like a high hydration dough for pizza, and thin crust, and I hate failure.
I came up with this cheat on the same method:
I found a thin, flat, rectangular steel pan that has a shallow rim on three sides and heavy wire handles on the two ends. It also has holes all over it like a perforated pizza pan. It looks something like this:
Mine is 11" x 14". It was also cheap. I got it at Dollar General for less than $5 when they stock a bunch of patio and gardening stuff in the spring.
You still have to cook the first side of the dough, then flip and top, but it makes it a lot easier than trying to drape raw dough onto a hot grill with bare hands.
The pan is also great for grilling asparagus, green onions, shrimp or any other small stuff you don't want to lose into the fire.
