The average US town has 6k people, so this is like relocating the population of 25 US towns to new, temporary housing.

Then you have to set up logistics to provide continual daily food and fuel to the new location for all those people. Then you have to relocate tanks which get about a mile per gallon of fuel, as well as people carriers, weapons, aircraft, missiles, ammo, field hospitals, blood and medical supplies, etc.

Armies rarely do "large scale exercises and maneuvers" precisely because they are so expensive.

Russia does multiple large scale exercises an maneuvers each year.

Russia also has a lot of basing nearby. For them, they're really only moving the units a few dozen kilometers from already established bases.

So for example, you mentioned a gallon per mile for a tank, which is indeed a realistic fuel consumption. The tanks are shipped by rail to nearby bases which is very shipped, and they then have maybe 200km to cover. 120 miles for 700 tanks is 84kGal of fuel, which is 420,000$ in fuel - that is, chump change.

Aircraft don't even need to be relocated. They're already there.

The rest, sure, but it's not as expensive as you'd think.

Looks like they decided to conduct their large scale exercises in Ukraine.

Not sure I follow why they would necessarily be doing large scale exercises and maneuvers if they weren't deployed to the Ukrainian border.

Also from what I understand a lot of these Russian troops are actually in Belarus as well.

You need to keep your troops occupied to keep readiness and to maintain training. You absolutely have to do large scale exercises and maneuvers multiple times a year. These deployments take the place of already-planned exercises, which actually were to take place in Belarus also.