gettext change level cost text

change_text_example.php

<?php

// Add this code below to your PMPro Customizations plugin - http://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/

add_filter( 'gettext', 'change_my_cost_example', 20, 3 );
/**
 * @link http://codex.wordpress.org/Plugin_API/Filter_Reference/gettext
 */
function change_my_cost_example( $translated_text, $text, $domain ) {  

        switch ( $translated_text ) {

            case 'The price for membership is <strong>%s</strong> now' :

                $translated_text = __( 'The price for membership is <strong>%s</strong> today.', 'paid-memberships-pro' );
                break;

            case 'and then <strong>%s after %d %s</strong>' :

                $translated_text = __( 'After your 365 day FREE listing only $15.00 per month.', 'paid-memberships-pro' );
                break;
        }

    return $translated_text;
}

Update, to adjust the membership price text. Please use https://www.paidmembershipspro.com/add-ons/pmpro-custom-level-cost-text/