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.