The 1976 Hino Freighter bus narrowly avoided bushfires and floods as it sat for the past 16 years at an Ewingar property, in the state's Northern Rivers region.

Now a campaign has been launched by the History Trust of South Australia to return the film star to her former glory.

Film director Stephan Elliott, who has been consulted on the project, said he and the cast and crew believed the iconic bus was lost to history before he was contacted by the History Trust.

"We had heard so many rumours about where she had ended up and had given up hope of finding her again," he said.

"But when they showed me the photographs, I knew immediately just by looking at the bumper bar at the front and the carpet inside that we had found it."

Mr Elliott said he was grateful for the "amazing discovery" and that Priscilla would be brought back to life.

"The film seems to carry through generations and this is a chance for possibly many more generations to feel its message of love, tolerance and living your true self every day," he said.

The History Trust plans to restore Priscilla to a roadworthy condition to be used on "special outings", and authentically return its interior to the glamorous style of the 1994 film.

Once restored Priscilla will find a new home at the National Motor Museum in the Adelaide Hills as part of an exhibition focusing on the film's cultural and social impact.

"Even in the 21st century, [the film] speaks to audiences of the virtues of respect for diversity and the great Aussie larrikin tendency for irreverence," History Trust CEO Greg Mackie said.

"It was first released into a world still grappling with the impact of HIV/AIDS and it immediately became a symbol of survival, the importance of love and respect, and of embracing difference."

A "Save The Queen" fundraising campaign was launched on April 12 by South Australian education, training and skills minister Blair Boyer.

The state government has pledged $100,000 to the project with the remainder to be raised through corporate sponsors, partners and donations with a target of $2.2 million.

"This project is a key investment in the National Motor Museum at Birdwood, where the bus will be located when restored," he said.

"I am thrilled we have been able to support the permanent public display of a significant piece of cinematic history."

More information on the campaign is available at history.sa.gov.au/priscilla