National Express is thought to be keen to renegotiate its contract
It is "unacceptable" that low-cost rail fares are easily available only to those with internet access, MPs say.
The House of Commons Public Accounts Committee said people without use of the internet or time to search should have the same access to low fares.
The MPs also said government plans to bring 1,300 new carriages into service by 2014 looked "over-optimistic".
Train operators said fare structures had been simplified and that tickets could be bought in a variety of ways.
The Public Accounts Committee report said that while the Department for Transport (DfT) set requirements for service frequency and punctuality it did not measure rising car park charges, complex fares and overcrowding.
Chairman Edward Leigh said: "It is unacceptable that you have to have access to the internet to get the cheapest fares.
"Those without such access, without time to search or who travel at short notice are stuck with paying through the nose.
"Fare structures should be easy to understand and the cheapest fare for a journey should be publicised and readily available at station ticket offices."
The MPs' report also said that despite plans to have 1,300 new carriages in service by 2013, only 423 had been ordered so far, with another 150 the subject of negotiations.
It added that as revenues fell some train companies could fail, but the government should still hold them to their financial commitments.
And it suggested some train firms might ask the DfT to "relax their contractual obligations".
"The department should explore all options and develop robust contingency plans to keep train services running in the event of multiple failure."
Rail, Maritime and Transport union leader Bob Crow said the government should step in now to begin re-nationalisation.
He said: "Rather than listening to the whinging from companies who have made a mess of their financial projections, we are calling on the government to step in now... to restore order to the railways."
£15bn will be invested over the next five years, the government says
Liberal Democrat transport spokesman Norman Baker said: "This is a damning indictment of the way the government has failed train passengers for over a decade.
"Prices have been allowed to mount to an unacceptable level with British passengers paying the highest train fares in Europe."
But transport minister Andrew Adonis said the government was committed to improving the railways and was investing £15bn on railways over the next five years.
"We will also hold rail companies to their contractual obligations and we will not allow most fares to rise by any more than 1% above inflation next year," he added.
Association Of Train Operating Companies commercial director David Mapp said: "Train companies have worked hard to simplify the fares structure and make it easier for people to get the best deals.
"Last year fares were simplified into three types - advance, off-peak and anytime.
The world-leading National Rail Enquiries service provides full information on fares, and passengers can buy tickets, including advance fares, through a range of channels including stations, the internet and by telephone."