Off-season is Mid April to Mid June and September to Med December. It is rather easy to find lower prices for air, hotel, renal cars, and tours during off-season times. You might run into some rain but the crowds will be limited an beaches less busy.
Whale season begins in November and goes through May. The "high" during the season for spotting whales is from January to March. When you go during the whale season you are often able to see whales from the beach and many hotels!