When I went to Ingapira there were no buses going directly over there. Luckily we had family that brought us. From what I hear now there are buses that go in and out of Ingapirca.
There are two buses that go from Cuenca to the town of El Tambo.from the you can catch the bus to Ingapirca every 30 to 45 minutes.
On your way back you can catch the bus from Ingapirca to Cuenca or to El Tambo.