Appreciated for your nice comments!

 
1. Roughly, it would be an acceptable deal if a balcony cabin costs you approximately $100/pp for those big ships (it’s more pricy for small ships). But there usually are big rooms to get significantly lower price if you are flexible to take “last minutes” cruises.
 
2. The best time to go South America is between December to March if you want to take the second segment between Santiago and Buenos Aires (summer in the south sphere), otherwise, it could be too cold and you may not be able to see penguins. It is very rear to see one ship to take all the three segments consequently. Last time of cruising all the three segments was in 2009 for all major cruise-lines (not very sure). Our cruise was a reposition of the ship; it’s said Carnival won’t do this again since the cruising conditions in Panama Channel are improving. One of the advantages in taking all three segments is saved the air fare to or from South America, which is usually expensive.
 
3. There are many agents/websites and cruise-lines themselves to book cruises. The key point is to find the lowest price around. You may check Crucon,  VacationToGo, etc. often. Cruise prices fluctuate (most cases are drops) more significantly than air tickets do, especially the last minute. We booked this trip from Crucon. Crucon usually give more on-boar-credit or a little bit lower prices but be careful Crucon charges $100/pp for cancelation even you cancel your trip months in advance.