Among the books that cost less than 1 dollar, how many were published by Berkley Trade?
book cost less than 1 dollar refers to price < 1; 'Berkley Trade' is the publisher_name;
SELECT COUNT(*) FROM publisher AS T1 INNER JOIN book AS T2 ON T1.publisher_id = T2.publisher_id INNER JOIN order_line AS T3 ON T3.book_id = T2.book_id WHERE T1.publisher_name = 'Berkley' AND T3.price < 1