TransferMarkt lists 27 players on the USA squad, so to achieve a value of 350m, the average player value only needs to reach a bit under 13m.
Pulisic is listed at 40m, Balogun at 30m. There are a handful other players in the 20m valuations, meaning the remaining squad players' valuations barely need to reach 8m or 9m to achieve that 350m number.
I see. I suppose my question should have been 'why are these countries rated ahead of Uruguay, Mexico, Senegal, Iran, Japan or Australia, when those countries have enjoyed far greater success on the field'. But I guess most of those countries have decent domestic leagues, while someone from the Ukraine or Serbia would be more likely to play in one of the big European leagues and thus be financially overvalued.