I think the last figure I saw for military spending was 650bn a year.

Of course if you cut that by half you'd lose a lot of workers many of those with families (in one respect you could look at the military as a jobs program, what was the last time the US had more than 10% of it's total military personal actually fighting a war).

Imagine if the military was converted to be mostly Corps of Engineers, building schools and roads and cafes, instead of building stuff to blow up.

The left opposition in Germany has actually recently run a bill in Parliament to establish a "Willy Brandt peace corps" next to our army. The line of thinking is that the army is well-regarded because of their development aid during foreign missions, and especially because of their help during domestic natural desasters. If that reputation went towards a peace corps instead, we would have an easier time arguing for less military spending.