We did not have any ZEDS between LIM and CUZ so we had to purchase. We were able to purchase on the flight to LIM as it had wifi onboard. It cost around $115 one way, we took the bus back via Nazca. Not sure if that helps, we spent no time in Lima, we stayed at the airport for an early flight out. I think there were open seats though. This was also at the end of May which is in the first part of the busy season.