TARP authorized up to $770 billion; by the time President Bush left office just $290 billion had been committed, and ultimately the final cost - after most was paid back - was around $25 billion. The CBO score was a 'worst case' - and remember, the CBO is the same group that said Obamacare would save trillions of dollars from the deficit!
TARP was a bad bill because it allowed dying companies to live - companies that SHOULD have died and made way for new, more efficient companies and healthier competitors. It was an attack on the free market process, not really a big addition to the deficit in the long run (about $25 billion added to the debt overall).