There is in fact no highway that accesses Aguas Calientes from Cusco, so having a bus for the whole journey is just not a choice. The trains are your best bet! The simplest way to get to Machu Picchu should be to go ahead and take educate to Aguas Calientes. https://machupicchutoursfromcusco17372.howeweb.com/27262929/machu-picchu-tours-for-dummies