If we're talking about right now, this very moment, then the S3 is infinitely cheaper than the SP30, since you can't even order an SP30.  Obviously at this point the advantage is to the S3 for everything.

The SP30 is a standard rack-mountable design with included PSUs.  Throw it in a rack, plug the two power cables into the PDU and the network cable into the switch.  Done.  You get charged standard $100/kw rates.  The S3 requires external PSU.  It won't fit into a standard rack, so requires shelves of some sort.

If I walk into a data center with an SP30 and say I need space for this, it's going to use about 3kw, they're going to say no problem.  I walk into that same data center with a bunch of S3s and say I need space, they're going to look at me funny.  Then they're going to charge me for custom space and setup fees and whatever else they want to handle my non-standard servers.

My point in all of this is that from a purely hosting standpoint the SP30 is going to win.  It's a single unit.  It's a standard rack size.  It's easy for the data center to deal with.  I already gave the S3 the price advantage for up front costs.  I did not amortize savings across the board, as that wasn't my intent with the comparison.  I considered each bolded section individually, and gave the advantage to whichever unit deserved it for that section.

Full disclosure: I own S3s.  I also owned an SP10 that I sold recently and replaced with S3s.  I've owned an S2 and S1s and U2s.  I do not own an SP30 because the unit came in far under the promised specs at a higher power usage than what the initial specs claimed.