How do I cache a page with file_get_contents?

I’m pretty new among you.

How do I cache a page with file_get_contents?

$site = file_get_contents('https://price.mysite.com/gold.php');

echo $site;

How can I print the output of this page to the cache file?

I want to show prices found here on another web page. Prices are updated every 30 minutes. On the page I will create, I want to use cache instead of constantly querying here. How can I do that?