Hello, @Artur,
Actually, by default when a user is on the single product page the price of the product will show, and if the user increases the quantity of purchase and add the product to the cart then in the cart page and on the mini cart the subtotal will appear so that user will know how much he will gonna pay for the product as you can see in the image of your site: https://postimg.cc/YvsQTDqF this is how it works by default.
Changes you want require extra customization. If you want paid Customization services submit a customization request to WPKraken team.
OR you can try with any third-party plugin which better meets your requirements.
Regards 8Themes Team.