How much would it take to end global extreme poverty? E.g., according to this page, Jeffrey Sachs estimated that it would take $175bn/year for 20 years to do so.

What are some other estimates?
The Economist (Oct 8th, 2016, online, PDF) attempts to answer this question.

It defines the global poverty gap as the amount we'd have to transfer to the world's extreme poor (defined as those living below $\$1.90$ a day, at 2011 PPP), in order to lift them to the $\$1.90$ a day threshold. 

The evolution of this global poverty gap from 1990-2013 is graphed below. As should be evident, at the current rate of decline in global extreme poverty, the world is on track to hit the World Bank's goal of completely eliminating extreme poverty by 2030. 



Nonetheless, even if there were no further progress and global extreme poverty stayed frozen at 2013 levels, 

a transfer of US\$78b a year would suffice to completely eliminate extreme poverty.

The Economist adds an important caveat:


  In reality, of course, money cannot be directed so precisely
  to the poor, nor transferred cost-free. In some countries, the infusion
  of money might also push up prices and currencies, making
  the endeavour more expensive. Nonetheless, this thought experiment
  illuminates the diminishing size of the problem. The world
  can afford to end poverty. Indeed, it might end poverty before it
  figures out how to measure it accurately.


$$$$

P.S. Note though that the reduction in global extreme poverty has been largely due not to transfers or aid of the sort envisioned by Jeffrey Sachs, but to economic progress, most notably in China.