Cost of the scheme has previously been put at US$3.3bn (£1.95bn).
The 210km line will link Mexico City to Querétaro in the north-west of the country.
The trains will be able to travel at speeds of up to 300km/h, saving two hours on current journey times. The line will have the capacity to carry 23,000 passengers a day.
Some 20,000 direct jobs are expected to be generated during the construction project.
The aim is for the line to come into operation in 2017.
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