The default format for woocommerce new customer order subject is below which can be modified with some limited parameter from woocommerce setting.
[Site Name here] New customer order (#Order id here) – Order Date here
As we sell some free products and get email alert for this. We need the email subject having the price so that the email subjects says all :P [You know what I mean]
To change all the order email subject woocommerce has filter which can be find here with documentation. Here is the code we are using to show the cart price total with the email subject.