Hi,
using a calculator to a specific products may involve in this kind of changes to the the bar at the bottom, to be able to give the customer the ability to customize the final product.
Adding to cart a product without specifying it attributes would not be a good practice . Anyway WooPrice is not associate directly to that change, maybe it is a feature of the installed theme you are using.
We navigate to the link specified by you, it seems that the ‘Add to Cart’ button below the product appears correctly.
Feel free to contact us anytime.
Best regards,
Naidi