If West Ham United are chosen to move into the Olympic Stadium at a crucial London Legacy Development Corporation board meeting next month, the now iconic Stratford stadium is likely to have cost at least £630m by the time it reopens in 2015 or 2016.

The club believes its tenancy bid remains the only viable solution to secure the long-term health of the Olympic Park and a future free of public subsidy. But some who will make the decision believe that, as the costs continue to spiral, it would be better to press ahead with the quicker, cheaper option of re-opening it as a multi-use stadium without football. The board remains split and will discuss at a meeting next month whether to press ahead with a full-scale conversion that would install retractable seats, a cantilevered roof and permanent hospitality facilities at a cost approaching £200m.

Even at the most conservative estimate the conversion budget would be £160m including £25m of contingency. But as contractors have yet to be appointed and the work is not fully costed, the overall cost could end up being £200m. Added to that are the cost of previous failed tender processes, lost revenue while the gates are shut and the £429m cost of building the stadium in the first place. West Ham delivered a "best and final" offer on Friday that is believed to represent an improvement on the £10m upfront contribution it originally put on the table, as well as rent of £2.5m a year and a claimed £6m-a-year uplift for the LLDC from increased revenue from naming rights and catering.

Sources close to the negotiations have disputed those figures and also point out that the LLDC is liable for around £2.5m in annual match-day costs if West Ham move in. Dennis Hone, the LLDC chief executive, has admitted it could be August 2016 before the first competitive match is played in the stadium. Documents released under the Freedom of Information Act showed that Newham Council alone spent £987,916 on the initial tender process that collapsed amid "legal paralysis" last year.

Insiders now believe that the stadium could be reopened for less than the £38m already put aside by the LLDC from the original £9.3bn public funding package if the decision were taken to drop West Ham and press ahead with an alternative option to appoint a stadium operator that could co-ordinate a programme of athletics, concerts and other sports. Under that scenario the stadium could open by spring 2014, looking much the same as it did during the Games. But the majority of the board, including the London Mayor Boris Johnson, is understood still to favour the West Ham option as long as they can make the numbers add up.

The total cost is more than three times higher than the £190m it cost to build the Millennium Stadium in Cardiff and considerably more than the £390m the Emirates ultimately cost, although still falls short of the £798m it cost to build Wembley after repeated delays and overruns.

It is understood that no contracts have yet been signed to take over tenancies at the stadium, even with UK Athletics, which is guaranteed 20 days a year of use under a heads of terms agreement signed last year, yet to sign a full legal document.

The former sports minister Richard Caborn said that the ongoing saga, labelled a "Stratford farce" by UK Athletics chairman Ed Warner last week, was the one serious mistake in the run-up to the Games. The option of building a stadium suitable for both Premier League football and athletics was definitively closed off in February 2007. "The Olympics were a fantastic success but this is the one area where we got it fundamentally wrong. I put the argument for a multi-sport stadium that would be like the Stade de France but 10 to 15 years on and I was shouted down," said Caborn.