Modify the display of free price in cart

wc-price-free-cart.php

<?php // only copy if needed
/**
 * Change cart price display for free products
 *
 * @param string $price_html the price display html
 * @param \WC_Product
 * @return string - updated pricing html
 */
function sv_wc_free_cart_price( $price_html, $product ) {
	if ( 0 === (int) $product->get_price() ) {
		$price_html = 'Free';
	}
	
	return $price_html;
}
add_filter( 'woocommerce_get_price_html', 'sv_wc_free_cart_price', 10, 2 );
add_filter( 'woocommerce_cart_product_price', 'sv_wc_free_cart_price', 10, 2 );