Call for Price lets you set a price but read Call for Price to get the customer to see a stated price but know there is a better price if they call.

To mask the price totally, you could use the function zen_products_lookup and identify if the product is a product_is_call = 1 and if so, mask out the price.

There is a display price function zen_get_products_display_price that can be customized to not show the price for certain products.

This section of code:
PHP Code:
    // If Call for Price, Show it
    
if ($product_check->fields['product_is_call']) {
      if (
PRODUCTS_PRICE_IS_CALL_IMAGE_ON=='0') {
        
$call_tag '<br />' PRODUCTS_PRICE_IS_CALL_FOR_PRICE_TEXT;
      } else {
        
$call_tag '<br />' zen_image(DIR_WS_TEMPLATE_IMAGES OTHER_IMAGE_CALL_FOR_PRICEPRODUCTS_PRICE_IS_CALL_FOR_PRICE_TEXT);
      }
    } 
tests to see if the product is Call for Price to add the image. You could change that to remove the return value below it:
PHP Code:
    return $final_display_price $free_tag $call_tag
to have the $final_display_price and $free_tag be blank so that all that is returned is the $call_tag when $product_check->fields['product_is_call'] = 1