Newegg offers the Eset 5-User Multi-Device Security for Windows, Mac, and Android for $49.99. Coupon code "EMCEMET66" cuts the price to $20. With $2.99 for shipping, that's the lowest total price we could find by $7. It includes mobile and tablet security and a GPS locator.
Also available is the Parallels Desktop 11 for Mac for $79.99 before coupon, $32 after, with free shipping. (A product key version is available for the same price.) That's the lowest total price we could find by $18. It allows you to run Windows 10 and Cortana on your Mac.