The Scottish Government has been accused of investing "not one penny" in a rail link between Edinburgh and the Borders since it came to power.
The line between Edinburgh and Galashiels could cost up to £295m
Lib Dem MSP Jeremy Purvis also called for plans to fund the bulk of scheme by a non-profit company to be scrapped.
Transport Minister Stewart Stevenson defended the government's approach to the project and choice of funding.
He said it would allow the "expertise and innovation" of the private sector to help deliver the scheme.
It emerged last week that the project costs for reopening the Waverley line could be as high as £295m - more than twice the original estimate.
The completion date for the scheme had also slipped from 2011 to 2013.
Mr Stevenson confirmed plans to use a non-profit method to fund the line between Edinburgh and Tweedbank near Galashiels.
However, Mr Purvis urged the Scottish Government to go back to funding the project directly.
"Since May 2007 not one penny has been invested by the government into this project and there has been a stall on the design process," said the MSP for Tweeddale, Ettrick and Lauderdale.
He said "urgent clarification" was needed over the funding method and the timetable for setting up the non-profit making company.
"So far the SNP have added confusion where there should have been clarity," he said.
"They have added delay where there should have been progress.
"We need to restore the funding, up front capital funding from the Scottish Government, for urgent progress for the construction of this railway."
MSPs voiced concerns about the funding of the project
Mr Stevenson defended the government's record.
"Much has been made of the issue of finance," he said.
"As advised last week, we intend to deliver this scheme using a non-profit distributing (NPD) model.
"This means we will use the expertise and innovation present in the private sector to deliver this public infrastructure project."
He said it meant any "excessive profits" could be reinvested for the good of the community.
"The Borders aren't the slightest bit interested in where the money is coming from," he said.
"The Borders are interested in it being spent to deliver a railway for the benefit of the people of the Borders.
"Our plans will ensure this railway is built on time and on budget."
Labour's Des McNulty said the funding method was "experimental" and "untested".
"Whether this project can progress is now dependent on the attitude of the banks to the funding package," he said.
He said the minister had given "no assurances" that funding could be in place for work to start within the lifetime of this parliament.
Tory Alex Johnstone said it was "disappointing but not at all surprising" that the project had suffered delays.
He also voiced concerns about the rail line covering only a "small area" of the Borders.