MIAMI -- The Florida Marlins' dream of a new baseball stadium may have been thrown a curveball Thursday, even as city officials offer some good news for local baseball fans on a possible new home for the team.

NBC 6 learned Thursday that at least one local government official believes a new ballpark can't be built without millions of dollars of taxpayer money, and that the cost of a new facility may have been grossly understated.

In the glow of the World Series championship, there were a lot of promises made about a new stadium by the team and some local politicians. All said the new all-baseball facility for the Marlins wouldn't cost taxpayers a penny. But now experts are analyzing the true cost and are coming to a very different conclusion.

On Thursday, the Miami City Commission said it wants the county to schedule a March referendum to ask voters to approve a half-cent sales tax in order to raise up to $250 million for the new ball park, to be added to the estimated $325 million cost originally estimated by the team.

"The $325 million is not the real number," Miami City Manager Joe Arriola said.

Discuss the proposed stadium

Arriola said he is figuring out the real cost along with County Manager George Burgess. The two men -- both veteran number crunchers -- say land acquisition costs were left out of the original estimates and that when added they greatly increase the total price tag

"The real number is around $450 million," Arriola said, adding, "At least 450 million. We have had people say that estimate might be short."

According to Arriola, the Marlins will be told they must also pay more for a new stadium and that the $137 million the team pledged in October is not enough.

The Marlins will be asked to contribute at least $150 million, NBC 6 has learned, and the money will have to be guaranteed by an outside party, because the team reportedly isn't strong enough financially to handle the cost on its own.

"It would have to be guaranteed by someone a lot more substantial than the Miami Marlins," said Arriola, referring to the new name the team will have once a new facility is built for them in Miami. "We are looking for at least Major League Baseball to guarantee this."

And Arriola added, "We are demanding that. We don't want a white elephant 10 years from now."

Asked if the stadium issue is "dead" without the guarantee, Arriola said, "As far as the city of Miami is concerned."

And he added that paying for a stadium is getting very complicated for all of the parties.

"It is a very tough sell," Arriola said. "We need to go to the public and tell them exactly what the truth is. And the truth is, (that) to do a turnkey operation, a stadium is at least $450 million."

NBC 6 has also learned that a new downtown location is being considered for the proposed new baseball stadium in addition to the Orange Bowl and the old Miami Arena.

The new, bayside location is located near the Omni complex, in the Pace Park area off Biscayne Boulevard.

A stadium would require about 15 acres, and city officials told NBC 6 the new site has emerged as the prime location under consideration.

"That area will be a great location for a stadium," Arriola said. "A lot of the property there is available and affordable. Obviously this is one of the reasons we would need a half-penny tax."

Arriola and Burgess are spearheading work on the stadium finance plan.

Arriola said the cost of a new ballpark will be a tough sell for taxpayers, but that since Marlins fans have indicated they want it built, they should know the truth about what it's going to cost and how much they'll have to pay for it.

The commission earlier approved the use of $73 million in previosly allocated tourism tax money for the new stadium.

Reported by NBC 6 Senior Correspondent Ike Seamans.