50 yards/450 Sq ft would cost 200$ if there are no extra charges, like stairs, or taking up the old carpet.
15 by 14 is 210 Sq ft which is 23.33 yards If installation is 5$ a yard Pad is 3$ a yard. Carpet you get a 12 $ a yard carpet (med. Grade) So right at about 500$ is what you'd be looking at