For a PhD in Econ for policy making jobs, such as Fed Reserve, the usual undergraduate training involves an Econ degree with a Math or Stat track/emphasis, or an Econ and Math/Stat major (many top universities have such a major jointly supported by the Econ and Math/Stat departments so that no need for double degrees), double majors in Econ and Math/Stat, or simply a Math/Stat major with some courses or a minor in Econ. With enough quantitative training at the undergraduate level and a degree from a top university (say top 30 or even top 50), it is possible to go from a bachelor degree to a PhD program directly without a master degree.
PhD program in Econ is pretty much all about training for doing research. So if your S is able to do a “serious” research with a faculty at his undergraduate institution and the quality of the paper is good enough for publication at an indexed journal (that is, a journal some people/researchers would actually read), it will really help. Of course, getting into a good PhD program also needs good GPA and good GRE.
Just getting into a PhD program in Econ is probably not that hard because there are many programs out there and they also take in (too) many students and have them teach intro macroeconomics or intro microeconomics (read inexpensive labor). But getting into a prestigious PhD program in Econ, say top 10, is an entirely different matter because some of their graduates are actually working on topics related to finance and may be hired as assistant professor of finance, instead of assistant professor of economics. At most universities, we are talking about 50% of salary differential.
Among PhD programs in Econ, I have seen best training and placement from Harvard, MIT, Princeton, Chicago, Yale, and Chicago (if I miss one, do not shoot me). UCB is also doing very well. If your S, down the road, is more interested in a PhD in finance or financial economics, Chicago is the powerhouse.
Note that the strength at the PhD level does not automatically translated into the undergraduate level. At the PhD level, it is all about research. At the undergraduate level, research is a substantially smaller component. Prestige, school culture, school tie, the quality of general education, professional development resources…are far more important.