Earlier quoted context omitted.
According to [1], for a family of 4 the poverty line is just under $24k? [1] http://aspe.hhs.gov/poverty/14poverty.cfm
Uh-huh. 4*8=32. You used 316 million as one of your multipliers, that presumably includes children.
Edit: from the poverty data [1] you could say that only ~45 million people get the full $8k, the rest starts to taper off at the 50 cents to a dollar pace. That means this would cost considerably less. $360 billion is the minimum. The cost out would be $3.9 trillion, but those extra $8k checks would be collected at tax time. A one job two adult household, the job holder would have to pay back all the $8k, but the partner wouldn't if they didn't make any money.