Melbourne could have trains and trams running at least every 10 minutes on every line seven days a week for a fraction of the cost of the North East Link.

Transport at that frequency would cost $2.1 billion over a decade, one eighth of the price to build Andrews government's signature toll road project.

The independent analysis by the Parliamentary Budget Office has been released just three weeks ahead of the state budget.

Before the 2018 state election the Greens promised to run 10-minute train and tram services from 6am to 9pm, seven days a week, a policy not matched by the Andrews government or the opposition.

An annual estimate of $214 million includes the cost of more drivers and maintenance staff, comprising $173 million for trains and $41 million for trams annually.