Display price on product page

You say

in the product parameters "display price = off"

but I don't know of such option for each product.
Could you do a screenshot of that page ?
As far as I know there is no option to say that you don't want to display the price for some products besides setting no price and changing the "free" word to something else via a translation override.
You would have to enter a specific price and then edit the file "listing_price" of the view "product" via Display>Views to remove the price display if the price is that specific price:
<?php if($this->row->prices[0]->price_value==11.11) return; ?>