As the Samsung S6 is integrated screen, when replace the screen it need to directly change the whole. At third party repair store the cost is about 150 USD or so. If ask for official after-sales it is more expensive, offering at about 200 USD to 250 USD. But if you know how to replace it by yourself, you can directly buy a Galaxy S6 screen replacement from online shop Cell Phone Ahe com for DIY, while the cost can be less than 100 USD.
Link for purchase: Galaxy S6 screen replacement