Let's call 1.47BTC $600 and $100 for a PSU. That's about 50 cents a gh. I paid about 65 cents a gh on the S4, but it's more efficient. A wash maybe?
Depends on your power costs, but I think the difference between 0.69W (S4) and 0.75-0.78W (Prisma) would take a long time to make up for the difference in price.
PSU (and controller too) is indeed an extra cost but not for everyone. I'm reusing my PSUs and have spare USB ports on on some cgminer-capable hardware here, so I'm saving money on that.
Another factor is resale value, I think S4 has the advantage here.
Since I am batch 1, I will post AMPs/Watts used and other information so we can compare to S4. Not sure how they can be the same one when is 1100W and the other is 1400W.