I'd guess about $10400, paid at $200 per week to the head of a household, plus an additional $75 per full dependent.

That works out as follows:

  Household Size | Annual UBI | 2014 Poverty
  ---------------+------------+-------------
               1 |    $10,400 |     $11,670
               2 |    $14,300 |     $15,730
               3 |    $18,200 |     $19,790
               4 |    $22,100 |     $23,850
               5 |    $26,000 |     $27,910
               6 |    $29,900 |     $31,970
               7 |    $33,800 |     $36,030
               8 |    $37,700 |     $40,090

That's a compromise. The UBI is less than poverty level, so that the conservatives can say that no one is getting a free ride, and people will still need to work to get by. But it's still around 90% of poverty line, so that the liberals can say that the government is still providing a great safety net.

There are 123M households in the US, for a population of 319M, so the total cost would be $200 * 123M + $75 * ( 319M - 123M ) per week, which is $39.3G, or $2.1 trillion per year.

The U.S. had official income of $3 trillion in 2014, so UBI would cost about 68% of the federal budget.

Like $3000 a month? Not enough to live in a major city, but you should be comfortable living somewhere in the US. Major city livin' is in short supply and is thus a luxury--- we'll never be able to have a high enough UBI for us all to live in NYC.