"It became clear it had to be a much bigger project.
"If we didn't have this wider project, we wouldn't get this external funding."
Mr Crimp said the project was achievable and costs would be funded from selling land and other council initiatives.
He said the impact on rates would not be more than laid down in the annual plan.
"The ratepayer was always going to have to cover the $900,000 loan. It is not planned that the ratepayer will need to contribute much more than that but until final funding flows are known - public bequests, grant funding and the like - we will not know if there is a shortfall and therefore what our next steps are."
The project has been "de-risked" by having a couple of phases, said Mr Crimp.
"There are a lot of aspects to bring together and we can complete the project in stages.
"If there is a shortfall, then the main landscaping can be deferred without impacting the main building."
Mr Crimp said that, while it seemed a big leap, it was a worthwhile investment to have a modern, unique acoustic venue in the district.
"To do just the strengthening, we would still have this building that's underutilised."
He said the council was excited about the project and people needed to decide whether it should proceed. "We need to make a decision as part of this annual plan. We can't delay the project for another year."