For what it's worth, "millions of dollars" is a pretty low bar. A million dollars in the US will get you _maybe_ 5 person-years worth of work from anyone at all competent (using the normal rule of thumb that an employees cost to the employer is about 2x salary once you take into account benefits, employer taxes, equipment, office space, etc).
So 10 million dollars will get you a 10 years worth of work from 5 developers. As an example, the PyPy project is 10 years old....
For JS, between the various browser vendors, the right number is probably closer to 300-500 person-years (see https://news.ycombinator.com/i... for an attempted breakdown). Figure $100 million as a low estimate. Chances are, the people involved are being paid more than $100k a year, so adjust the estimate up accordingly...