A local group is warning that the introduction of a new downtown arena in Edmonton will cost hundreds of millions of dollars more than what has been projected. The group, Speak Up Edmonton, has now launched an advertising campaign showing what it believes the arena could actually cost in tax dollars.

The group has launched billboards across the city, stating a new arena will cost "$400 million tax dollars, number that has not been reported. But the group admits that is a conservative estimate.

"The reason it is wrong is the total cost of the project is $600 million dollars," said group spokesperson Lorne Humphreys.

Speak Up Edmonton says its cost estimates are on the conservative side, providing an overview of numbers that haven't been discussed, but will hit the bottom lime.

City council says it cannot comment on the specifics of the group's estimates.

Councillors will be brought up to date on negotiations between administration and the Katz Group next week.

"I think what it speaks to is the lack of information, what the full cost of this project might be," said City Coun. Don Iveson.

The largest unknown portion of costs for the area include things such as sewers, roads and LRT service.

"You have a development that includes a much broader development, so it becomes difficult to ascertain the amount of infrastructure that goes into that broader development that needs to be looked into," said sports economist Dan Mason.

NHL Commissioner Gary Bettman recently warned the public of the costs the city will face if a new arena is not built.

"There is not question about it they are not going to stay in this (Rexall) building," he said. "I already engaged in one effort to save the Oilers in Edmonton, I really don't want to have to go through a second one -- this team needs a new building."

An update on the negotiation between city administration and the Katz Group will be made public on March 2nd.

Speak Up Edmonton also plans to present to council that same day. The Katz Group has declined to comment on the numbers discussed by Speak Up Edmonton.

The Katz Group originally hoped construction would start by early 2011, but so far has only managed to push land rezoning efforts through.

At present, Daryl Katz is committing $200 million to the project, and is hoping to secure another $125 million from the city as well as $100 million from other levels of government.

With files from Kevin Armstrong