Over €55 million has already been spent on the BusConnects plan in Dublin.
Figures released to Fianna Fail TD John Lahart show that the National Transport Authority has so far pumped €55.2 million into the project.
Spending on route redesigns - including the core bus corridors and outer routes - and a "next generation" ticketing system have accounted for most of the millions.
The cost of the project is expected to run up to a whopping €2 billion.
Deputy Lahart believes the costs need to be broken down and illustrated better throughout the project, however.
He told the Irish Times: "They haven’t broken down the costs into the different sections so we don’t know how much the route changes cost, for example.
"There are what appear to me to be extravagant elements which are unnecessary and overengineered."
He also said that consultation with the public had "not been satisfactory", adding: "You can’t help but come away from time to time with the feeling that these routes have been desktop designed without a field trip."
Plans for the 16 main bus corridors involved in the plan were published last November, which would involve the felling of over 3,000 trees and the purchase of parts of over 700 existing front gardens on some main routes.
The Dublin South West TD added that he was concerned that there may be some "underestimating" of the cost of these redesigns, which he believes "could balloon".
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