I have traveled to Antarctica and the Arctic with Australian based Aurora Expeditions.http://www.auroraexpeditions.com.au/expeditions/category/antarctica-cruises
I found their expedition staff very considerate to photographers even though it was not a pure photographic tour.
They were very happy to take directions when in zodiacs and always tried to land us as much as possible when the conditions were right.
They also gave us announcements over the PA for whales, but a lot of people slept though it due to the long days.
I would travel with them again.
Josh Holko, a Melbourne based photographer who frequents LuLa has teamed up with Aurora Expeditions and Daniel Bergmann for a few photographic only voyages.
You can find detail on his website http://www.jholko.com/
Regarding cheaper last minute voyages to Antarctica, yes if you have plenty of time to hang out in Ushuia, you can get last minute deals. Often these are on very large ships that do not allow landings for all passengers each day. You really want a ship with 100 or less passengers due to the antarctic treaty that limits the number of tourists in one area to 100 (I maybe incorrect, it may be slightly higher). So the cruise ships that have 200-500 people are not really worth the cheaper price. Better to save more and go on a trip that will both maximise your time and photographic opportunities.
The only reason I did not go on a 100% photographic trip like LuLa's expeditions is by the time I could negotiate time off work I missed out and waiting lists were too long.