Add recurring period to pricing

functions.php

<?php
add_filter( 'edd_purchase_download_form', 'aihrus_edd_purchase_download_form', 10, 2 );
function aihrus_edd_purchase_download_form( $purchase_form, $args ) {
	$id    = $args['download_id'];
	$price = edd_get_download_price( $id );
	if ( 0 == $price ) {
		$price         = '&#036;' . $price;
		$replace       = 'Free';
		$purchase_form = str_replace( $price, $replace, $purchase_form );
	} elseif ( class_exists( 'EDD_Recurring' ) && EDD_Recurring()->is_recurring( $id ) ) {
		$period = EDD_Recurring()->get_period_single( $id );
		if ( 'never' != $period ) {
			$replace       = $price . ' per ' . $period;
			$purchase_form = str_replace( $price, $replace, $purchase_form );
		}
	}

	return $purchase_form;
}
?>