function woo_custom_order_button_text() {
$cart_total = wp_strip_all_tags( wc_price( WC()->cart->total ) );
return sprintf( __( 'Place order %1$s', 'text-domain' ), $cart_total );
}
add_filter( 'woocommerce_order_button_text', 'woo_custom_order_button_text' );