Families of people who signed up for the war got large amounts of money. The transfer of money from the Russian national wealth fund into the economy, together with the shortage of workers, increased salaries.

[Edit] People didn't keep that money but spent it so others profited from that money too.

This is what happens in wars - beside war racketeers - salaries go up. There is a lot of research on how German profited from WW2 (and before) for example for most of the war. WW2 too seems most researched from what I see on how everyone profits until things get worse and end.

a "war chest" is usually saved by the state (by under-investing into everything civilian) and then given back to the working-class population as salaries, sign-up bonuses, investment into logistic infrastructure. If you look up the stats - there was a real-estate boom in the early years of the was as many families could finally take a mortgage. Now many cannot pay for it because the bonuses and soldier salaries "don't last" hence companies like "Samolyot" are now in trouble.