July 2012: I was quoted $3,100 from a Sandy, Utah Honda dealer.
The Owners Manual (Civic 2005) only indicates the battery is warranted "up to the full price." However, Honda claims the warranty is 8 years or 80,000 miles. My car had 89,000. Symptoms: IMA and engine light.
I called Honda to complain about the price. Honda, in turn, called the dealer, and the price was lowered from the dealer's $3,100 to $500, which I paid.
There are other web forum entries of owners that claim they got 100% replacement. Honda told me they handle complaints on a case-by-case basis, so there may not be consistency.
Five states have modified their laws to require the Honda warranties cover $150,000.
Summary: $3,000 seems to be the average quote for a hybrid battery. If you are willing to complain, Honda seems willing to drop the price.