For the year is $ 99.99.
For that much money you could buy the iWork suite for both your iPad and Mac, and never pay again.
What you would pay for 2.5 years is equal to the cost of Final Cut Pro X.
Also, consider the fact that you'll need to be connected to Skydrive, which requires an internet connection.
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The app store shows In-App purchase of a 1-Year subscription for $99.99
The issue is not everything in word or excel transfers well with pages and numbers. There really is no great substitute for office, and that is what all businesses use.