Would need lot of extra fuel to raise altitude for an escape trajectory. Fuel either brought up the gravity well at launch or later refueled in orbit. Of course not all satellites are designed to allow in-orbit refueling. Maybe an reusable orbital tug might be something that someone will come up with.

It doesn't have to be one vehicle. You can launch 10 falcon 9s (perhaps even using the same booster) and have them take turns pushing.

Do you realize that 10 F9 flights means 10 new second stages and on those second stage someting has to sit and that something whatever that is - is completely dwarfed by ISS and it would have to be a new dedicated vehicle consiting of mostly fuel just to deorbit the sucker in one go.

Original plain AFAIR was to use several Progress vehicles.

And going to graveyard orbit with something like ISS is not just a few whole times more difficult but at least an order of magnitude more.

The ISS weighs 450 tonnes.

Ten Falcon 9s (with 8 tonnes to GEO each, expended) couldn’t move it into a parking orbit. There literally isn’t enough current lifting capacity on Earth to do this.

You're trying to calculate this with weird units. ISS escape velocity orbit would require about 3200m/s delta-v. Yes, with chemical rockets this is like 800 tons of fuel. But you don't really need the high thrust of big chemical rockets. You could do it with ion engines which have a specific impulse between 10x to 100x higher than chemical rockets, bringing the total cost way down. It would take much longer, but it could be done.