This is all anecdotal but...
I bought...
1TB WD Green EARS HDDs in 2010 for $70.
2TB WD Red HDDs in spring 2014 for $89.
1TB WD Black HDDs in fall 2014 for $90.
Just spot checked the same drives...
1TB WD Green EARS HDDs go for $57.
2TB WD Red HDDs go for $89.
1TB WD Black HDDs go for $71.
So prices are slowly falling but I don't think that we're going to see the rapid falls we were accustom to in the last decade due either to technological constrains or consumer demand, likely both.
From 2000-2005 we went from 20GB to 500GB drives, a 25x growth in 5 years but in 2010 we only had 2TB drives which is just a 4x growth. It's 2015 the largest consumer HDDs you can get from WD, Seagate, and HGST are 6TB, 8TB, and 10GB respectively. That's 3-5x growth for the 5 year period. Why has growth slowed? Is it a technological constraint or a lack of investment?
In the early 2000s you could only play music and movies you possessed so there was a big demand for storage space for all your ripped CDs and DVDs. In 2007 Netflix introduced online streaming and today we have thousands of choices for streaming video or music on demand which combined with cloud storage options negated our need for high capacity drives. I think the fact that people are opting for 120GB SSDs over 4TB HDDs demonstrates that the consumer need for extremely large hard drives is in decline.
In the past the HDD makers were very competitive but if you look at WD, Seagate and HGST today you can see they're no longer competing on drive capacities. HGST is the only one that even bothers to sell a consumer grade 10TB HDD. Western Digital has been diversifying for years; first it was portable backup solutions, then NAS drives, NAS solutions, Surveillance and Data Center drives, and just today they announced they're buying Sandisk, a major SSD player.
I think the industry as a whole is moving away from HDDs and for that reason they nolonger need to compete so ferociously on price points.