NowebNolife

Решил данную проблему, получением subtotal напрямую из хука 'woocommerce_before_calculate_totals'

add_action( 'woocommerce_before_calculate_totals', 'dynamic_discount_based_on_price_cost_change' );
function dynamic_discount_based_on_price_cost_change( $cart_object ) {
    //get cart
    $cart_items = $cart_object->get_cart();
    //get cart total
    $totalprice = array_sum( wp_list_pluck( $cart_items, 'line_subtotal' ) );
 }  
}