<What is this steamer addon that Alton is using called and how much does it cost approx?>
To answer your two questions:
1) This is called a "collapsible steamer" or "folding steamer". They are traditionally made with stainless steel, but some new ones are made with plastic:
2) They cost between $5-$30.
You didn't ask this for this, but I personally do not prefer this kind of steamers.