pmpro-change-price-by-date.php

<?php   // do not copy this line.
/**
 * This recipe does will change the price for a membership by the date
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function pmpro_checkout_sale_price( $level ) {

	$month = date( 'n', current_time( 'timestamp' ) );
	if ( in_array( $month, array( 1, 2, 3 ) ) ) {
		$level->initial_payment = number_format( $level->initial_payment + 20, 2 );
	}
	return $level;

}
add_filter( 'pmpro_checkout_level', 'pmpro_checkout_sale_price' );

/* change price by month text */

function nicer_pmpro_level_cost_text($text, $level)
{
global $pmpro_pages;
$month = date( 'n', current_time( 'timestamp' ) );
if ( is_page( $pmpro_pages['levels'] ) && in_array( $month, array( 1, 2, 3 ) ) ) {
	//Change this text below to match your needs.
	$text =  number_format( $level->initial_payment + 20, 2 ) . " includes 20 as a late checout fee.";
}

	return $text;
}
add_filter("pmpro_level_cost_text", "nicer_pmpro_level_cost_text", 15, 2);