Two things:
1) you'd still budget 125k a man-year? Why? That's only needed for devs in SV, NYC, London and other places with mad rent, besides - all you're gonna get in these places are fresh university grads and hipsters, not seasoned people with actual experience that tells them to not use a two months old JS framework for something that is supposed to live long.
2) Why limit it to USA? Other countries have decent programmers too, with way lower cost of employment. 60k is going to fetch you quality in Germany, 30k in Eastern Europe.
Besides, the best way to finance all of this, other than pressuring government to procure only/preferred open source is some rich startup exiter putting a couple billion dollars into some sort of trust fund and pay the development from the interest.