The new LEGO Batman Movie 30521 Mini Batmobile Polybag set is now available at Toys R Us stores in America. They are available at $3.99 each. Alternatively, you can also try to build the set yourself with pieces that you already have. Official LEGO instructions are available here. Thanks to forum member ResIpsaLoquitur for the news.
LEGO 30521 Batmobile