According to some Wikipedia research “De-orbiting a geostationary satellite requires a delta-v of about 1,500 metres per second (4,900 ft/s), whereas re-orbiting it to a graveyard orbit only requires about 11 metres per second (36 ft/s).”
Huh, wouldn't have guessed it to be that much, but it makes sense. De-orbiting gets cheaper the higher your orbit is and a geo stationary orbit is high, but not that high.