For the same size SSD and advertised bus speed, there is already a huge price performance variance. SSDs vary greatly in both IO operations per second and total IO operations (lifetime).
There are SSDs that have worse IOPS than a HDD, but in most cases HDDs cann't touch SSD IOPS specs.
On the other side: A great SSD might have a better lifetime (IO operation total) than a cheap HDD; however it is still to be proven that an SSD could match a quality HDD in lifetime.
Whenever these price comparisons come up, I get the feeling that there is a huge bias in favour of the statement that article wants to make. i.e. If its about the falling price of SSDs, then compare a low spec SSD with a high spec HDD. If you want to argue for HDD, do the reverse.
As things stands both have their place, and you should be careful about what you buy in both cases. e.g. WD-Green for laptop, but WD-Red for a NAS (yes there is a difference). For SSDs only my budget would force me to buy an EVO instaed of an EVO Pro. (I only mention WD and Samsung to be able to give concrete examples).
In my (humble) opinion neither SSD nor HDD will be able to replace the other, before some other storage technology comes along and blows them both away. Although that tech might be a descendant of one or the other (memristor? crystal/optical?).