Light rail proponents have ridiculed an $860 million price tag for a transit line to be built from Canberra's north in to the city.

A transport study released by the ACT Government today said the Gungahlin to Civic line would cost $700-$860 million to build, while a bus rapid transit along the main commuter corridor could be installed for $300-$360 million.

Environment and Sustainable Development Minister Simon Corbell announced the estimates today but gave no guarantee the ACT Government will go to the October election with a commitment to either transport option.

But Mr Corbell was immediately accused by light rail proponents of overstating the cost of the 13km Civic to Gungahlin link.

The ACT Greens said the government needed to get on and commit to a public transport option for the corridor.

The chair of ACT Light Rail, Damien Haas said the tracks would need to be "plated in gold" for the figure to be anywhere near $800 million.

Mr Corbell said the costs would become clearer as more detailed analysis was done and that the next stage of the project was asking Canberrans which option they preferred.

"These are large scale projects and we must make sure we do the detailed investigation before we make the decision," he said.