Russia's 2019 military spend was 65 billion USD, or 58.6 billion EUR. Clearly they are not blowing through an entire year's defense budget in three days (that would be over 100x the usual rate of spend!).
Or another sanity-check figure: Russia's entire 2020 GDP would pay for only 67 days of war at this run-rate. In other words, the country is using over 500% of its productive output on the war (a neat trick without any imports!)
For reference, in 1940 the United States spent 1.64% of its GDP on defense. In 1945 it spent 37.19%.
I'm as hopeful as anyone for Ukraine to survive this awful war with her sovereignty intact, but we must be realistic.