Nicer level costs example. Add this to your active theme's functions.php or a custom plugin.

nicer_pmpro_level_cost_text.php

/*
	Nicer level costs.
*/
function nicer_pmpro_level_cost_text($text, $level)
{
	global $pmpro_currency_symbol;
		
	if(pmpro_isLevelFree($level))
		$text = "Membership is free.";
	elseif($level->initial_payment == $level->billing_amount)
		$text = $pmpro_currency_symbol . $level->initial_payment . "/" . $level->cycle_period;

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