Hello,
You can find pricing at the below link. That's the link from the Norton eStore. It runs $49.99 for an addtional 25 GB of storage. Each purchase stacks onto your prior purchased space and is sharable between Norton Online Backup and the online backup portion of Norton 360 as long as you use the same Norton account between the two.
http://buy.norton.com/estore/mf/productDetails/listPriceGroupId/1000000/productSkuCode/20052315/productShortName/norton-online-backup/sourcePageType/Category/categoryCode/Backup_and_Restore_Sub_Category/priceGroupId/1000000/slotNo/3/
Also if you look under Special Promotions there may be a holiday special going on.
