The Ai Weiwei's Circle of Animals/Zodiac Heads exhibit on the Rose Kennedy Greenway cost about $100,000, but last summer's floating art exhibit cost a whole lot more.Watch the reportIt was originally budgeted for $500,000. Instead, the final bill came in at $1.7 million, and that didn't include the amount the artist, Janet Echelman, received from private donors for her design work.That $1.7 million paid for engineering, materials, installation and removal of the exhibit last fall."We will defend this project until the end of time for the impact that it had," Greenway Conservancy Chief of Staff Michael Nichols said. "It got the private philanthropic community excited and members of the public excited."It was the biggest chunk of $2.8 million the Greenway Conservancy spent more than 18 months on public art and Nichols emphasizes very little of that money is tax dollars."It covers roughly 12 projects, and is almost entirely privately fundraised," Nichols said. "And the only part that is publicly fundraised are competitive art grants. So money that's already been set aside for the use of public art."Forty percent of the conservancy's budget comes from the state Department of Transportation, but Nichols said it only pays for horticultural and maintenance costs. What about Executive Director Jesse Brackenbury's salary, which climbed 30 percent in just three years to $217,000?"His salary is paid for completely out of non-public funds; it's through private sources," Nichols said.He said the hikes were approved at open meetings by the Board of Directors. But do the art installations take money away from other charities?"This is what makes Boston a cosmopolitan city," Nichols said. "This is what everyone likes to joke, a world-class city. "So are you saying the future projects may well cost a lot more than this?" NewsCenter 5's Janet Wu asked."If there are the private resources available to pay for a project on the scale of Janet Echelman, we would seek to identify them," Nichols responded.Transportation Secretary Stephanie Pollack said she will review an ongoing internal audit on the matter before deciding whether to renew the Greenway Conservancy's two-year lease.Echelman told Wu late Tuesday afternoon she received no money from either the conservancy or taxpayers. Her work was supported by private donors that she declined to identify.