There is no TABLET that can play BLACK OPS II. Now there is a service called OnLive which is now working with STEAM, as the ONLIVE servers does all the 'gaming' and all it does is stream the video to your screen, so it doesn't matter if your on a Smartphone, Xbox, Tablet, whatever you can play many different titles without any need to reinvest in hardware.
That said, MOBILE platform costs 2X the desktop price, and no it doesn't matter you want low settings your still demanding 50FPS or better, and that doesn't happen by just putting on low settings. A common desktop system that can play 1080P, High settings, and 45FPS or better across any game, starts at $700. That is buying a PC today AND expecting to play today's titles and forward. Mobile side, this translates to $1200 or better normally, because the ADDITION of a addon video card to the laptop is the only way the game will play, onboard video isn't cut out for 'gaming' only to perform the other 90% other things (Word, Email, Youtube, etc.).
Due to the additional costs, AND that most people making post like yours are more familiar with consoles, AND consoles last 10 years as compared to 5 years for PCs before you HAVE to replace it, I would refer you back to going console if you want the 'cheapest thing that will play Black Ops II', which is a PS3 or Xbox 360 for around $149.