The price is fine...
According to your post you are a single user.. meaning you want Kaspersky for personal use..
Why not use Avast Antivirus Free Edition, it as good as any paid antivirus software out there, even better
www.avast.com
For your second query you can install as many OSes on a single PC, however take care of the order in which you install the OSes, during installation, the OS being installed might overwrite your previous OS's bootloader, rendering it inaccessible.