revisiting this topic...
ok, so 4TB regular hard drives can be had for about $200-300.
1TB SSD is over $400
The highest capacity 2.5" hdd available today is 2TB. 2TB laptop drives go for $100 and up, while 1TB laptop drives go for about $50 and up, $70 and up for high performance (7200 RPM) drives.
Micron has just introduced a "budget" line of SSDs in the 2.5" form factor that is slower than top of the line SSDs, but still more than 10 times faster than the fastest laptop hard drive, at $149 MSRP for 512GB and $299 MSRP for 960GB. That's 6 times the price for 10 times the performance. The gap is closing.
I'd agree that I don't see SSDs replacing desktop HDDs any time soon for long term and off line storage, but I think they will mostly survive as external devices, either as portable drives or as NAS.
Added 11/6/15 - I've started to see 2TB laptop drives priced below $90, at the same time, the price of a Samsung 2TB SSD has dropped from $1,000 to $750. Also, Micron has announced they will no longer make SSDs with less than $240GB capacity because they expect the market to move to 1TB and higher.