I guess it comes down to how much you we are willing to accept as a good savings after you factor in all the driving time, added wear and tear on your vehicle, hotel, meals, etc.
Out last two trips were out of Halifax, direct. Feb 06, we all flew for $420 per person. This past July we flew direct form Halifax again for $460 per person. We are booked again for this Feb, direct from Halifax again, for $616 per person. The cost to fly for our next trip is considerably more than our last two. I suspect more people are taking advantage of the exchange rate, which keeps demand up, and therefore prices.
For me, I'm not sure a 20 hour drive is worth the savings. It adds two full days to your vacation and seems like it would be a very uncomfortable way to end a very busy week.
Direct flights are great and well worth it compared to the inconvenience of a 20 hour drive to from Portland, imo.