State Treasurer Rob Lucas revealed the amount paid by the previous Labor Government as $1.5 million after a decade long confidentially agreement had expired.
The contract long rumoured to be in the millions, which included additional expenses like hotel accommodation and first-class return airfares, only required that Armstrong take part in the Down Under Classic prelude and not necessarily the UCI WorldTour race.
"South Australians have a right to know this information. We tried to release it straight after the election but couldn't legally under the terms of the contract, which explicitly prevented either party from publicly disclosing its details for 10 years," Lucas told local media.
Armstrong did race the TDU itself after a contentious anti-doping pool exemption was granted by the International Cycling Union.
He also raced the following two years, though details about possible appearance fees for those events will not be revealed until those confidentiality agreements have run their course.
Lucas questioned the amount paid to Armstrong and the previous government's reluctance to recover the money.
"They (Labor) need to come out of hiding and justify two things," he said. "One is why would they pay so much money and secondly why didn't they try and pursue some of that money on behalf of the taxpayers of South Australia?"
Labor MP Tom Koutsantonis defended the payments, saying the return on investment was calculated at $30 million.
"Was it controversial? Yes, it was," he said. "Should he (Armstrong) have paid the money back? Absolutely. But was South Australia the focus of the entire international cycling world while he was here? Yes, it was."