I was getting drawn into trying to understand the OP calculation and network behaviour, but isn’t StoreCost really going to be determined by:
the perceived value of a SafeGB in fiat
the maximum PUT cost in Safecoin, which will be SafeGB in fiat divided by the exchange rate of fiat per Safecoin
[Aside: For the network to be viable, the maximum farming reward needed to secure an additional GB storage must remain near or below the maximum PUT cost per SafeGB in fiat (over a sustained interval, as short term fluctuations would not cause the network to fail immediately). The actual farming reward will be as low as possible, while enough to ensure it is near or slightly above the PUT cost per SafeGB in fiat.]
The monetary figures in Safecoin can’t easily be calculated because they depend on the Safecoin fiat exchange rate which is damped, and perhaps bounded, by the characteristics of the network, but determined by multiple unpredictable factors.
The best guide we have will I think be other cryptocurrency projects that have been around for a long period, such as bitcoin and Ether. I think those are probably good examples because SAFE Network is similar in breaking new ground (bitcoin) and creating new applications and services through additional features and desirable characteristics (Ethereum).
So when the network launches and Maidsafecoin is converted to Safecoin there will be quite a wide range of possible values while people try to determine the speculative value of the coin over different time periods. I’d expect the coin to be in demand, with fiat price rising but very volatile initially, and then rising in fits and spurts over the early years as demand grows, applications expand, reputation matures etc. Eventually it will remain within a less volatile range and the range may rise or fall according to external changes. That is all just speculation and guesswork though, so don’t trust it!
But putting figures on any of that will be unreliable guesswork IMO, which carries over directly to any Safecoin denominated figures that depend on estimates of things denominated in fiat (such as the cost of cloud storage).