Non-numeric price value to "Ask seller"

Hi.

I have a question.

So, users can write something like “contact me directly” or “call for price” directly into the price field.
Here is what I am trying to achieve:

When an user puts non-numeric character in price field, then regardless of what they have written, I want to show “Contact the seller” on the product page.

Would you happen to know how I can do this?

Thank you