ST. PETERSBURG — Tampa Bay Rays principal owner Stuart Sternberg said Wednesday he expects the team to contribute more than the $150 million he mentioned last year toward building a proposed $892 million ballpark unveiled this week.

"I absolutely know it will grow from there, but I also know it's not going to be multiples" of $150 million, Sternberg told the Tampa Bay Times' editorial board.

So, Sternberg was asked, could the team's share be as much as half the project cost?

"I don't envision it," he said.

That's not an answer Tampa Mayor Bob Buckhorn wants to hear. Noting that he doesn't speak for Hillsborough County officials, the mayor said there's an assumption that a stadium would be a "shared burden," and to him that means the Rays ought put in at least half of the money required for ballpark.

"It's a step," Buckhorn said of Sternberg's comment that the team's contribution will top $150 million.

"A baby step," the mayor added. "I think the reality is that unless the Rays are able to get to close to half, this will be a very difficult transaction to complete."

During a 55-minute discussion with the editorial board, Sternberg said what the Rays will be able to spend will depend on, among other things, what the team gets for naming rights on the ballpark, how many businesses or individuals sign up as founding sponsors for a $1 million a year or more, how much the new ballpark drives additional sales of season tickets and whether and how much corporate support promises to grow.

"We have a number in mind for all these things," he said, though he didn't say what that number is.

Last November, Sternberg had floated the possibility of the Rays putting $150 million into a Tampa-based stadium — the same figure the team discussed in 2008 during the unsuccessful proposal to build a new stadium on the St. Petersburg waterfront — as a working number.

COMPLETE COVERAGE: Rays unveil their plans for an Ybor City ballpark

But he said then and again on Wednesday that the team's share of the costs for a new ballpark would be driven by projections on increased sales of season tickets, growth in sponsorships and the success of a private sector effort in Tampa to round up additional corporate support.

"Things change," he said. "We have a better estimate on costs. We thought it was going to be less at the time, but more importantly, we're seeing" that the business-driven Tampa Bay Rays 2020 effort in Tampa is "getting some positive feedback and excitement."

Rays 2020 is working to increase corporate support for ticket sales, sponsorships and naming rights for the ballpark.

"We're hopeful that we can raise incremental revenue that the Rays earn on an annual basis of somewhere between $20 million and $30 million" from those three sources, said Ron Christaldi, a Tampa attorney who formed the nonprofit Rays 2020 group. "Increasing the bottom line," he said, would give the team "additional revenue to put toward construction of the stadium and a good team on the field."

The effort is a work in progress, Christaldi said, but the response has been encouraging, with several parties showing serious interest in naming rights, and he expects the plan unveiled Tuesday to fuel interest.

The team envisions a ballpark that's small (28,216 seats) by Major League Baseball standards — but one with:

• 30-foot-tall glass windows that can be opened in the outfield and behind home plate to let in a breeze on pleasant days.

• A translucent roof with an arty shade canopy with a swooping shape that's already been compared to a wing, a bird and a swimming ray.

• A new mix of seating types and options.

• 21 viewing platforms and social gathering spaces, plus play areas that kids and residents can enjoy even when the team is not playing.

THE RAYS VISION: A ballpark with windows that open, a translucent roof, spaces to play — and a $892 million price tag

The Rays and their supporters hope their design inspires additional business support for the team — something that is lower than Major League Baseball averages at Tropicana Field and something the Rays say needs to rise — thus reducing the amount that Hillsborough County, the city of Tampa and the Legislature would be asked to contribute.

"Every business is going to have to make their decision," Sternberg said. "However, I need to, at the very least, and then some, have a sense that there is a desire from the larger business community to believe that this is the right thing for them."

Contact Richard Danielson at rdanielson@tampabay.com or (813) 226-3403. Follow @Danielson_Times