Scottish Labour yesterday hit out at the "colossal waste of money" after the Scottish Government confirmed spending of £29.91m up to last month, with an estimated £120,000 still to be incurred.
The total includes £8.5m on buying land and making additional compensation payments to the original owners - of which just £360,000 was recouped in subsequent sales.
GARL, which was intended to connect Glasgow Airport with the city's Central Station via Paisley, was scrapped by the Scottish Government in 2009 on cost grounds.
The Herald revealed last month the final parcel of land purchased for the scheme at £840,000 was sold back to its original owner for £50,000.
But figures released by the Scottish Government yesterday in response to parliamentary questions showed that two other owners, Kenyart Ltd and J&M Taylor (Holdings) Ltd, were also able to buy back at reduced prices.
Labour MSP James Kelly said: "This is an astonishing waste of our money and exposes the financial lunacy of cancelling a rail link that was supported by the business community as a boost to the economy.
"It begs the question why was the Scottish Government so keen to get rid of the land given the huge losses it has incurred.
"Surely, as a country, we have an aspiration to link our biggest city and our biggest airport - why did it not hold on to the land so it could be built in future instead of pursuing a scorched earth policy?"
The Herald revealed how the Scottish Government sold four plots in Paisley to airport parking firm Airlink Group for £50,000 after it failed to find a buyer at auction. The Government had bought the land five years earlier from an Airlink subsidiary company for £840,000.
Yesterday it emerged the Government bought land from developer Kenyart Ltd for £115,000 and sold it back for £99,600. It paid property firm J&M Taylor (Holdings) Ltd £240,000 and sold it back for £124,500.
Total land sales and compensation for loss of business amounted to £8.532m. Land sales after the scheme was scrapped recouped £359,500.
The previous Labour-LibDem administration approved GARL in 2006. The project, estimated to cost £170m, was to have included a new 1.2-mile section of track over the M8 to a purpose-built station at the airport. The branch line was scrapped in 2009 on cost grounds.
A spokesman for the Scottish Government's Transport Scotland agency said: "Around £176m of capital expenditure was saved as a result of the Scottish Government's decision not to proceed with the branch line element of GARL.
"Since the cancellation of GARL, routes along the Paisley line have benefited from £230m investment in rail infrastructure improvements alongside a new £430m fleet of Class 380 trains now operating in Ayrshire and Inverclyde."