The current best guess is in excess of $3.65 million reports the Arizona Politics blog.
Wednesday, Arizona's Politics reported on the legal costs incurred by Arizona taxpayers because of the partisan battle over the Arizona Independent Redistricting Commission - that article noted the costs - to the taxpayers - had "exceeded $3.4 Million." The AIRC has now provided breakouts of legal fees it has paid over the past four years, and it turns out that the legal bill is now at $3,649,239.
The actual cost could have been, and most likely will be, much higher.
There are presently three live cases against the AIRC, all from either Republican lawmakers, or Republican-philic interests. Surprisingly, the AIRC has spent THE LEAST in outside legal expenses on the Arizona Legislature v. AIRC case about to be decided by the Supreme Court.
This is partly because it is a Constitutional challenge that did not require much time-intensive (costly) discovery, and partly because the U.S. Supreme Court expert Seth Waxman surprisingly agreed to represent the Redistricting Commission pro bono. That saved Arizona taxpayers somewhere between $300-500,000.