If you’ve been waiting for the option to buy more than 100GB of storage on SkyDrive, your wait is over. You can now buy an extra 200GB of storage space for $100/year. As you can see in the screenshot below, the space you purchase is added on to whatever you already have (in the Total Space column).
The current price per GB is $0.50/year vs. ~$0.60 per GB/year for Google Drive. Not a huge difference but a little less. Though Google Drive makes up for part of this by providing the first 15GB free (vs. 7GB for SkyDrive).