Answering my own question in the hopes that it helps someone else - if you walk out to the main road from the hotel, turn left and walk about 5-6 blocks, you'll get to what the locals call "Terminar" (where the speed bump is). This is where all the taxis and collectivos wait for people to go to Ollantaytambo

It is S/1.50 if you take a collectivo (van), but then you have to wait until it's full before it leaves. A taxi should be S/15-20. I was told by my taxi driver that taxis start appearing there at about 3:30 a.m.