Hamilton's new mayor is "horrified" by the $27.4 million paid by the previous council for staging the city's V8 Supercar race over the past three years.

The figure released today is made up of $20.3m for set-up costs, $5.1m for operational costs and a $3.5m cost to change the event to a new promoter, following the collapse of promoter Caleta Streetrace Management earlier this year.

The sum did not include "commercially confidential" amounts such as event sponsorship payments.

Recently elected Hamilton Mayor Julie Hardaker said today she and some councillors were "deeply concerned" about how much the event has cost since it started three years ago, leading them to appoint an independent person to audit certain systems and processes within the council.

"It is fair to say that when council saw the figures in the way in which this latest report shows them, they were quite horrified."