Apple posted more details of its new iCloud online storage offering and Macworld has the details including pricing. After the initial free 5 Gigabytes, 10 GB more costs $20 a year, 20 Gb costs $40 and 50 GB more costs $100. Including the 5 GB you get free, that's $1.33 per GB per year at the low end, $1.60 in the middle and $1.81 at the high end.
This sets Apple apart in two ways. It's pricing is relatively low compared other providers at the start. But like a fog that dissipates as it rises, Apple's good deal melts away as you buy more storage. Apple is the only company that becomes less price competitive as you buy more and it is the only company that increases the cost per GB as you add. Everybody else gives a better or the same deal to people who buy the most space.
Dropbox is $120/year for 50 GB, or $2.40 per GB, and $240 for 100 GB, also $2.40 per GB. Much more expensive than Apple, period.
SugarSync is $50 for 30 GB ($1.67), $100 for 60 GB ($1.67), $150 for 100 GB ($1.50) and $250 for 250 GB ($1). Trails Apple at the low end but a better deal at the high end.
Google's space is very, very cheap at just 25 cents per GB per year all the way up to 1 TB for only $256. Google does have a music locker service in beta and, if you have an Android phone, an awesome auto-back up of photos. But doesn't have the same kind of broad back up and syncing service as the others. Perhaps someone will write an app that uses the Google Docs upload interface?
People have written apps like JungleDisk for Amazon's s3 service but the storage is not cheap, at $1.68 per GB per year. There is an option to store with less redundancy, so data could be lost, for $1.12 per GB per year.
Amazon's own cloud drive service, which includes a lot of free space if you buy your music there, is 20 GB for $20 and 50 GB for $50, or $1/GB on up to any huge amount you require.