Are you kidding me?! The one for $12.50 is all you need for even 8 bots.
I have the $15 one, and I can run a PvPGN server, multiple websites, MySQL server, PHP, Teamspeak, and torrents. And I can run 2 bots with ease (I don't usually load more than 2).
Do you have any idea how cheap that is? If you expect to get 768 RAM for cheaper than $20, you are NOT getting a Windows VPS. You'll have to get a Linux VPS, and those won't run most bots. Most Linux servers don't come with a GUI, so I'd hope you know how to start one or use the bots without a GUI.