MILLWALL chief executive Steve Kavanagh said promotion is worth £6millions to the club – but warned increased costs are likely to offset any financial gains.
The Lions sealed their place in the Championship when Steve Morison scored an 85th-minute winner against Bradford at Wembley last Saturday.
Championship football will bring bigger crowds and more TV revenue, and Kavanagh said the club "want to be competitive" in the second tier.
"There's a quoted figure of round about £6million, but I would suggest your costs go up by £6million-plus," Kavanagh said.
"There's income but there's a different cost base. We're competing against teams with 60/70 million-pound budgets now on the playing side.
"We have to go out there and compete, we want to be competitive. That's what we're working on. Yes, there's an uptick in income, but there's probably an uptick-plus in costs."
Kavanagh met the rest of the Millwall board on Wednesday to discuss strategy ahead of preparations for next season. Chairman John Berylson was also jetting into London later in the week.
Kavanagh would not be drawn on whether Millwall could break their transfer record this summer, the £800,000 they paid Derby County for Paul Goddard in December 1989.
"People have to go beyond just pure transfer fees," Kavanagh said. "Wages nowadays are as important as transfer fees. If a player is out of contract then the transfer fee is the wages, because they are in demand.
"This idea of it's all about transfer fees – it isn't. A number of good players are out of contract because players let their contracts run down.
"The price of the transfer fee goes into the wages, it's a mish-mash. We have our budget, be it wages or transfer fees, and that's what we'll work to."
Meanwhile, Kavanagh revealed Millwall's players were on bonuses to win promotion from League One.
Some of the squad – including Shaun Williams, Jed Wallace, Aiden O'Brien, Ben Thompson and Tom King – jetted off to Marbella on Sunday, with Las Vegas the next stop on the promotion party.
Kavanagh said: "The whole squad was on a bonus, I'm not going to say what that was. It was a collective effort, that desire and team spirit showed right the way through to the end of the season, into the play-offs and the final.
"That team spirit was vital in getting us through, as well as a bit of quality."
Image: Millwall FC