Air Serbia is the cheapest bet. As of a couple days ago, pcr test is still required to enter russia. But the only people who wanted to see the test were the airline gate attendance. Nobody at passport control asked to see it.
This is probably my tenth trip to Russian. It's was a new passport with a new Visa though.
I flew Air Serbia, I had a 12 hr layover where I did enter the country to do a little sight seeing.
My flight landed at SVO at 01:00. I'm pretty sure I was the only US citizen on the flight