functions.php

/**
 * Hides the Ninja Forms add-ons' prices in the cart and checkout pages
 *
 * @param  string $text
 * @return string
 */
function wc_nf_hide_price( $text ) {
    $text    = strip_tags( $text ); // Strip HTML tags <span class="amount"></span>
    $pattern = "/\s\((\D{0,2}\d{0,3};)\s?\d+([\.,]\d+)?\s?[\D+]?\)$/";

    /**
     * Pattern explained
     *
     * $pattern  = '/\s';                  // Any white space/tab before the price
     * $pattern .= '\(';                   // The price parenthesis
     * $pattern .= '(\D{0,2}\d{0,3};)';\s? // Currency sign on the left
     * $pattern .= '\d+([\.,]\d+)?';       // Decimal amount
     * $pattern .= '\s?[\D+]?'             //Currency sign on the right
     * $pattern .= '\)/$';                 // The price parenthesis
     */

    return preg_replace( $pattern, '', $text );
}
add_filter( 'wc_nf_addons_cart_option', 'wc_nf_hide_price' );