I ran these numbers long ago. I think 24’ tall would be plenty. It is what is used to secure substations etc.
If they lowered the wall to this height, they would need a hell of lot less in the way of foundation.
http://www.utilityconcrete.com/Substation-Security-Wall-Panels
I just saw a Federal soundwall bid where the cost psft is $22 psft, so at 8 by 24 feet you are looking at $540 per lineal foot. plus foundation, excavation and set up.
ftp://ftp.odot.state.or.us/Bridge/CostData/CostDataBook2013/cost_data_2013.pdf
Thanks for the info. The original post presumes a 10 ft below grade barrier to stop tunneling, which I included...I think in reality the wall would be maybe 5 feet below grade, so a person couldn’t just dig down 2 feet and shimmy under the wall. I don’t know where 50 ft came from (maybe Trump said it), but that’s pretty extreme.