Premier Mike Rann says construction will begin immediately on the new Royal Adelaide Hospital.

He's revealed South Australians are locked into a 35 year deal, worth almost $2.1 billion.

That's $400 million more than the original price.

The blowout has been blamed on delays and an increase in the hospital size at the old railyards site on North Terrace.

Save the RAH campaigner Jim Katsaros claims the total cost will be more like $5 billion thanks to hidden costs like remediation bu tHealth minister John Hill says that's not the case.

"He keeps making claims that are proven to be false time and time again. The cost of remediation is built into the contract of the developers and it will be covered by the 1.85 construction costs of the hospital." 

Photo:Getty/Getty Images News/Jamie McDonald/Stringer