It would be an apples and oranges comparison to some extent. The Soviets were able to skip some expensive research and production steps that the Americans went through by exploiting intelligence gained from espionage [0].

[0] https://en.wikipedia.org/wiki/Soviet_atomic_bomb_project

I'd be interested in that as well. The US program was expensive in part because they were trying to do it as quickly as possible, didn't know exactly what a finished bomb would look like and basically pursued every possible method for isotope separation at massive scale all at once.

A program that just pursued plutonium production and separation to produce implosion devices would presumably be a lot cheaper (though still massively expensive in absolute terms, obv).

> The US program was expensive in part because they were trying to do it as quickly as possible,

The US also was trying to just do it, whereas the USSR had the benefit of stolen research.

Well, thanks to the likes of Julius and Ethel Rosenberg the Russians were no doubt able to save a helluva lot of time and money.