WooCommerce: Cart price override with text

We have a bunch of products with either:

• No price
• Zero price

We made them purchasable with the built-in hook but the cart still displays them as having a 0 price during checkout.

We'd like the cart & checkout summary to display "Special order" or any other text, but it seems WooCommerce invalidates text-based prices.

Tried this : WooCommerce: Add product to cart with price override?

The above works fine with a number override, but when tried with a text override it defaults back to displaying a 0 price.

Why? These products are built-to-order and the shop admin will update price after talking to customer/supplier.

expanding on Helga's answer, here's the full code that changes the prices to 'to be determined' on cart pages, checkout pages and order confirmation emails too. Text kept different so people can spot where each filter goes.

    add_filter( 'woocommerce_cart_item_price', 'filter_cart_item_price', 10, 3 );
function filter_cart_item_price( $price, $cart_item, $cart_item_key ) {
    if ( $cart_item[ 'data' ]->price == 0 ) {
        $price = __( 'Special Order', 'yourtheme' );
    }
    return $price;
}

add_filter( 'woocommerce_cart_item_subtotal', 'filter_cart_item_subtotal', 10, 3 );
function filter_cart_item_subtotal( $subtotal, $cart_item, $cart_item_key ) {
    if ( $cart_item[ 'data' ]->price == 0 ) {
        $subtotal = __( 'To be determined', 'yourtheme' );
    }
    return $subtotal;
}

add_filter( 'woocommerce_cart_subtotal', 'filter_woocommerce_cart_subtotal', 10, 3 ); 
function filter_woocommerce_cart_subtotal( $cart_subtotal, $compound, $instance ) { 
    $cart_subtotal = __( 'To be determined 4', 'yourtheme' ); 
    return $cart_subtotal; 
}; 


add_filter( 'woocommerce_order_formatted_line_subtotal', 'filter_order_item_subtotal', 10, 3 );
function filter_order_item_subtotal( $subtotal, $item, $order ) {
    if ( isset( $item[ 'line_subtotal' ] ) && $item[ 'line_subtotal' ] == 0 ) {
        $subtotal = __( 'To be determined 2', 'yourtheme' );
    }
    return $subtotal;
}

add_filter( 'woocommerce_order_subtotal_to_display', 'filter_woocommerce_order_subtotal_to_display', 10, 3 ); 
function filter_woocommerce_order_subtotal_to_display( $subtotal, $compound, $instance ) { 
        $subtotal = __( 'To be determined 6', 'yourtheme' );
    return $subtotal; 
};

add_filter( 'woocommerce_get_formatted_order_total', 'filter_woocommerce_get_formatted_order_total', 10, 2 ); 
function filter_woocommerce_get_formatted_order_total( $formatted_total, $instance ) { 
        $formatted_total = __( 'To be determined 8', 'yourtheme' );
    return $formatted_total; 
};