Why is an IRS audit so costly?

Answer 1

It's only "costly" if you didn't file a correct return in the first place.

I've been audited 4 times. Two were correspondence audits and were cleared by mail with no changes. One cost me about $100 and the other got me a refund of $75.

Answer 2

As bostonianinmo said, it all depends on WHY you are audited. If they simply need documentation of a legitimate deduction, the 'cost' is likely to be a postage stamp. If you wind up challenging a decision in court, the attorneys are the main cost.