Hardcode price for all items in Google Product Fee

functions.php

<?php

add_filter( 'woocommerce_gpf_feed_item_google', function ( $feed_item, $product ) {
	// The regular price of the item.
	$feed_item->regular_price_ex_tax = 1000;
	$feed_item->regular_price_inc_tax = 1200;
	// Set these to NULL if no sale price, or the sale price if required.
	$feed_item->sale_price_ex_tax = null;
	$feed_item->sale_price_inc_tax = null;
	// Set these to the sale price if it exists, otherwise the regular price.
	$feed_item->price_ex_tax = 1000;
	$feed_item->price_inc_tax = 1200;

  return $feed_item;
}, 10, 2 );