The detailed project report (DPR 11.4MB zip) for the Airport Link was released some time back and is pretty much along the lines reported over the last couple of years in the media. The problems I had with the plan still stands.
According to the Infrastructure Development Department website, the shortlisted bidders are
1. Pioneer Infratech Pvt. Ltd. & Siemens Project Ventures GmbH
2. Lanco Infratech Ltd. & OHL Concesiones S.L.
3. L&T Transco Ltd.
4. Reliance Infrastructure Ltd. & CSR Nanjing Puzhen Rolling Stock Co. Ltd.
5. ITD – ITD Cem Joint Venture
It will be interesting to see whether any of the shortlisted bidders will agree to build the line without a really significant subsidy/viability-gap funding given that actual passenger traffic numbers at BIA is significantly short of the projections given in the DPR (prepared by DMRC in Oct 2007). For example, 2010-2011 annual traffic was projected to be 17.2 million, while the reality is in the range of 11 million. Projections for future years look even more wildly optimistic - 30 million by 2016-2017 would require a really radical expansion of the airport which BIAL is not even comtemplating.
It is also not clear if the alternate possibility of building a commuter rail using the existing railway tracks that pass pretty close to the airport was properly evaluated.