Write SQL query to solve given problem: What is the average replacement cost of the films under the category of "Horror"?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT AVG(T3.replacement_cost) FROM film_category AS T1 INNER JOIN category AS T2 ON T1.category_id = T2.category_id INNER JOIN film AS T3 ON T1.film_id = T3.film_id WHERE T2.name = 'Horror'