ACT opposition claims that the Labor-Greens parliamentary agreement would create a $2 billion black hole have been laughed off by the government.
On Friday, Opposition Leader Zed Seselja said the Liberal calculations, using Treasury costings, revealed the cost of keeping Labor in power amounted to billions.
But Treasurer Andrew Barr attacked the claims as ''wildly inaccurate'' and proof the Liberals weren't ready to form government.
The Liberals added Labor's $1.2 billion election promises to the $800 million agreement. Mr Seselja said Canberrans should know the price of Labor keeping power.
''We have used costings under-taken by Treasury, and taken out doubled up costs such as light rail to get a fair and complete picture of the costs,'' Mr Seselja said.
''[It equals] about half the entire budget of the ACT, or about the equivalent of the entire health and education budgets combined.''
Mr Barr said the budget impact from the election commitments made by Labor and from the parliamentary agreement would be $68 million in 2013-14.
''Zed Seselja's analysis on the cost of ACT Labor's election commitments looks like it was written on the back of a drink coaster - after a few too many beers,'' Mr Barr said.
''It beggars belief that a party that forgot to include CIT in its education policy, couldn't figure out whether its health plan was over four years or five, and failed to submit its $7 billion health and $3.6 billion education policies for independent scrutiny, would try to take the moral high ground on costings.''
He said the 2012-13 budget had a provision for capital works of about $190 million - against which the election commitments of ACT Labor and other parties was allocated.
''Light rail will be funded in partnership with the private sector,'' Mr Barr said. ''The cost won't be met upfront from the ACT budget, and will be spread over the life of the project.''