According to Fortune magazine and other sources, right now the direct military operational costs are running about $1.7bil per day. But that cost increases exponentially as Russian forces move deeper into Ukraine and lose more men & equipment, while consuming more munitions, fuel, and food.
Other losses to their domestic economy due to sanctions bring the total price tag to roughly $21.7 bil/€20 bil per day :
https://www.consultancy.eu/news/amp/7433/research-ukraine-war-costs-russian-military-20-billion-per-day
But how long Russia can contine paying for Putin’s disaster isn’t exactly clear. The Ruble is already virtually worthless, and their investment bond status has been downgraded to junk by Moody’s and Fitch. Some anyalysts suggest Russian gold and foreign currency reserves will run out in as little as 10 months, others say they could hang on up to 2 years.
The only sure thing is that Ukraine has much less time.