Those cost estimates are high even if one considers just what the conflict is costing Russia.
The Pentagon estimates Russia's cost is closer to $300M per day and that's likely a large number because many armored vehicles ("tanks") being "disposed of" due to poor planning, poor logistics, and poor leadership/strategy. Also, there are major bites from losing battleships. Ukraine has lost little of its navy (LOL) and has made much better/judicious use of their armored vehicles. To claim Ukraine is spending close to what the Russian's are spending simply is not supported by the evidence. Feel free to provide contrary evidence.
To be sure, Ukraine is heavily relying on support from allies and that no doubt makes them able to prosecute this war "on a shoestring". That said, Ukraine has a distinct advantage of fighting on their own turf (cue Napoleon and the Nazis attempting to defeat Russia in the last two centuries, Persia attacking Greece over two millennia ago, etc.). It's true that logistics is what wins wars, but Russia has not (yet) shown that it is in command of its logistics. No doubt, Russia has "deeper pockets" than Ukraine, but their pockets definitely have holes.