One interesting twist- when I was doing my table I was mostly thinking of SATA in terms of the high capacity 3.5″ drives, where you can get a 1TB drive for ~$90 and a 1.5TB drive for $120. So that is actually $.08/GB (which I rounded up to $.1). But a very interesting in-between solution is to go with the commodity 7200RPM 2.5″ drives. The fancy 10k/15k RPM SAS drives are always worse performance/$, but a $60 250GB 7200 RPM 2.5″ drive gives you pretty much the same IOPS. Plus I’ve seen 2U server designs that can fit more than 25 in a single box (as compared to ~8-10 max 3.5″ drives).
So if you aren’t trying to maximize capacity in a 2U unit you can either do-
10×1.5TB 3.5″ drives, 15TB storage, 750 IOPS, $1200, 0.625 IOPS/$
25×250GB 2.5″ drives, 6.2TB storage, 1875 IOPS, $1500 1.25 IOPS/$
Which represents twice the performance/$ at a cost of less than half the capacity/$. But again, if you weren’t going to be able to use that capacity anyway, its a great trade-off.
Alternatively in the same price range you could get two of those SSDs if you data-set is really small-
2×64GB SSDs, .13TB storage, 6600 IOPS, $1400 4.7 IOPS/$
So the SSD performance/$ is still better, but the capacity is so small that its unlikely to work for many applications.