For example on Newegg a vanilla 7200 HD from Western Digital, at 1tb, will run you $50. The lowest cost 1tb SSD will run in the mid $300s. A solid 7x difference.
In less than two years we'll see consumer retail 1tb SSDs for $150 to $200. What's actually going to happen, more than a violent price plunge pushing 1tb down to $50, is capacity will soar while prices fall more reasonably than the article indicates. So you'll be buying 5tb SSDs for $300 in three or four years. The difference is the friction the SSD makers will insert into the market, when it comes to falling prices; ie the difference between what they could sell them at, and what they actually will sell them at. The race will be to higher capacities first, then as capacity saturation nears, the bottom will fall out of lower SSD storage tiers on pricing.