Hi,
I’m not sure I really understand your question, but it seems that you want to set a product (WooCommerce?) to status = draft if the price is set to zero? This would have the effect that any products with a zero price would be hidden from end users.
If this is what you want, you can solve it like this:
1. Create a workflow with “Post saved” as the trigger
2. Set up three filters. (a) “Post type” is one of “Product”, (b) “Post status” is one of “Published” and (c) Custom field “_regular_price” Equals 0
3. Set up a Change status action that sets the new status to “Draft”.