Which movie title has the lowest movie rental in the horror category?
the lowest movie rental refers to min(rental_rate); the horror category refers to category.name = 'Horror'
SELECT T1.title FROM film AS T1 INNER JOIN film_category AS T2 ON T1.film_id = T2.film_id INNER JOIN category AS T3 ON T2.category_id = T3.category_id WHERE T3.`name` = 'Horror' ORDER BY T1.rental_rate LIMIT 1