Yes, it is free to switch Windows 10 in S Mode to Windows 10 Home . . .
Here is the method:
Open the Settings App
Go to Update and Security - Activation
In the Switch to Windows 10 Home or Switch to Windows 10 Pro section, select Go to the Store. (If you also see an "Upgrade your edition of Windows" section, be careful not to click the "Go to the Store" link that appears there.)
On the Switch out of S mode (or similar) page that appears in the Microsoft Store, select the Get button.
After you see a confirmation message on the page, you'll be able to install apps from outside of the Microsoft Store.