Amazon offers downloads of Symantec Norton Security 2015 5-User 1-Year for Windows, Mac, Android, or iOS for $19.99. That's the lowest price we could find by $10.
Amazon also offers it via a key card bundled with a $10 Amazon Gift Card for $29.99. (You must add both to your cart to get the discount.) Plus, Prime members bag free shipping. (Non-members can spend over $35 to bag free shipping; otherwise, it adds $4.48.)