Cost is not an issue compared to convenience. From 1992 to about 4 years ago, I used mostly Linux (desktop and servers). Now I have gone down the dark path of living in APple's little walled garden (except for servers). I don't care if Google Drive is a lot cheaper than iCloud: with OS X Mountain Lion and an iPad, using Apple's iCloud storage is just more convenient. BTW, with OS X Mountain Lion it is strange that for some apps the default storage is iCloud and not your local disk (although obviously you work from a local copy).
That said, it will be interesting to see apps built on top of Google Drive APIs.
I agree that cost is not the main factor here, because the real battle is being fought in the free tier of all these services anyway.
However I'm not sure iCloud wins on convenience unless you live entirely inside an Apple ecosystem (and even if you do, do you want more lockin than you have already?).
For me convenience is about universality: which ever company gives me the best experience across every platform is the one that wins. iCloud fails because Apple has a fundamental conflict of interest in making your experience better on iOS vs everything else. Of course, they also can employ anticompetitive measures to ensure that all other services are worse on iOS so I guess it sort of evens out. Google has some similar issues but I think they have a much broader interest in making their service universal than Apple does. Mainly, I don't really trust Google to get the quality up to par ... so many of their services seem to get 95% of the way there and never get the final bugs ironed out because they are "good enough". But we'll see.
That said, it will be interesting to see apps built on top of Google Drive APIs.