Opposition councillors have backed Milton Keynes Council's plans to spend an extra £620,000 on the new coachway.
The money is to come from growth funding awarded to the city by the government.
The new terminal is being developed by Milton Keynes Council with £2million from the Homes and Community Agency, the new name for English Partnerships.
The council claims the extra £620,000 is needed to ensure the bus station is an iconic gateway into the city.
MK NEWS revealed last week that the state-of-the-art facility, near junction 14, was due to be completed this spring, but now might not be completed until summer 2010.
Cllr Chris Williams, transport spokesman for Milton Keynes Council said the designs for the building, unveiled in April 2007, had turned out to be more expensive than estimated.
"We discovered that we were unable to meet the costs of that particular building and decided that because it is so important we would go back to the Government.
"Around a month ago we were awarded another £3million of growth area funding from the Government because transport schemes have generally been well run and organised.
"The cabinet has agreed that we will use £600,000 of this money to top up the budget for the coachway to meet the environmental standards and high specifications we wanted."
Opposition councillor David Hopkins, environment spokesman for the Conservatives, added: "The Government specifies that it is for infrastructure so it would seem to me that it is a very suitable way to spend it.
"If we are going to do it we have got to do it right, then it is more likely to be used and to provide a good entrance into Milton Keynes."
Roger Bristow, environment spokesman for Labour said: "At the end of the day I think it is probably better to get it right than to get it now.
"But in future we need to make sure that the costs of building are calculated far more carefully at the beginning."
The plans will now go out to tender again, subject to the funding being finalised.
The council anticipates for the coachway to be completed by spring/summer 2010.
It will have a striking roof canopy with roof lights above the coach bays, a heated waiting area for 100 people, a café, a convenience shop and a ticket office for the National Express Group.
Meanwhile commuters will have to spend a second year using the temporary coach station built off Silbury Boulevard in Campbell Park.