Add account creation fee for new users or users who have not renewed their membership within 1 month.

my_pmpro_add_account_creation_fee.php

<?php

// Copy from below here...

/**
 * Add account creation fee for new users or users who have not
 * renewed their membership within 1 month.
 */
function my_pmpro_add_account_creation_fee( $checkout_level ) {
	// If user currently has a membership level, don't apply fee
	if ( ! empty( pmpro_getMembershipLevelsForUser() ) ) {
		return $checkout_level;
	}

	// Get user's most recent enddate
	global $wpdb;
	$user_id = get_current_user_id();
	$enddate_query_result = $wpdb->get_row(
		"SELECT enddate
		FROM {$wpdb->pmpro_memberships_users}
		WHERE user_id = $user_id
		AND status <> 'active'
		ORDER BY id DESC
		LIMIT 1"
	);

	// If this is a new user or enddate is over a month old, add fee
	if ( empty ( $enddate_query_result ) || ! isset( $enddate_query_result->enddate ) || time() > strtotime( '+ 1 month', strtotime( $enddate_query_result->enddate ) ) ) {
		$checkout_level->initial_payment += 15;
	}

	return $checkout_level;
}
add_filter( 'pmpro_checkout_level', 'my_pmpro_add_account_creation_fee' );