Change the level cost text of a PMPro level for an A/B test.

my_pmpro_level_cost_text_for_ab_test.php

/*
	Set a cookie when users enter a specific page.
	(You would setup Google Experiments or your A/B testing software 
	to send 50% of visitors to this page.)
*/
function my_wp_set_cookie_for_ab_test() {
	if(is_page('pricing-2')) {
		 setcookie('ab_test_group_2', 1, 0, COOKIEPATH, COOKIE_DOMAIN, false);
	}
}
add_action('wp', 'my_wp_set_cookie_for_ab_test');

/*
	Now change the price shown if the ab_test_group_2 cookie is set.
	
	Note that this only changes the price when displayed. It will not
	adjust the actual price charged. For that, use the pmpro_checkout_level filter.
*/
function my_pmpro_level_cost_text_for_ab_test($cost, $level) {
	global $pmpro_currency_symbol, $pmpro_pages;
	
	//no cookie, we don't need to change anything
	if(empty($_COOKIE) || !isset($_COOKIE['ab_test_group_2']))
		return $cost;
	
	//check for a specific level
	if($level->id == 1) {
		//if on the checkout page, act like the lower (real) price is a discount
		//note that this assumes the currency symbol is on the left like USD
		//and would need to be adjusted for your prices
		if(is_page($pmpro_pages['checkout'])) {
			$cost = str_replace($pmpro_currency_symbol . '100.00', 
								'<span class="text-formatting: strike;">' . $pmpro_currency_symbol . '200.00' . '</span> ' . $pmpro_currency_symbol . '100.00',
								$cost);
		} else {
			//otherwise increase the price to 200 from 100
			$cost = str_replace('100', '200', $cost);
		}
	}
	
	return $cost;
}
add_filter('pmpro_level_cost_text', 'my_pmpro_level_cost_text_for_ab_test');