The cost of a new bridge across the Firth of Forth has been estimated at between £360m and £400m.
Work is currently under way on the existing bridge
The price would be dependent on design and the incorporation of a tram link, while the construction of a rail link would increase it to about £580m.
The figures were included in a consultants' report on the feasibility of building another bridge.
The report also said that planning and construction would take a minimum of nine years.
The latest assessment was an update of plans first drawn up in the early 1990s.
The new, bigger, crossing would be just to the west of the existing bridge and have a 1,375m central span.
The revised proposals which are based on a suspension structure, have now been put to the Forth Estuary Transportation Authority (Feta), on which four local councils are represented.
The final phase of roadworks on the existing Forth Road Bridge is taking place this weekend before a summer pause.
Work on a second phase of the £3.2m resurfacing will resume in September.
The work is being suspended for two months to prevent traffic jams during such annual events as the Royal Highland Show at Ingliston and T in the Park.
Contractors have been working between 1800 BST on Fridays until 0600 BST on Mondays.
Phase two will get under way on Friday, 3 September, and last until the work is complete.
Feta convener, Councillor Mike Rumney, said: "Carrying out such a major contract was always going to have led to disruption, frustration and delays to drivers.
"But, hopefully, by restricting works to weekends and completing it over two phases, we've kept that to a minimum."
To ease congestion during the weekend roadworks, train operators ScotRail and bus firm Stagecoach agreed to run extra trains and buses.