We did Buenos Aires to Valparaiso Xmas of 2002 on Celebrity Zenith. We had a great time and especially liked days at sea almost every other day.
Buenos Aires was amazing and we really liked the glaciers and many of the Chilean ports of call. The highlight for us was the two penguin rookeries. All said, I'd do it again in a heartbeat.
Our airfare was in the $800 range round trip open jaw from Portland, oregon.I hope this helps.