Talks over British entry into a major EU defense program have been deadlocked for weeks over the question of money. Negotiators might just have found a way out.

With a Sunday deadline looming, the two sides are exploring “alternative payment models” to bypass the row over the entry price for London to take part in joint procurements financed by the EU’s €150 billion Security Action for Europe loans-for-weapons program, according to an EU diplomat briefed on the negotiations.

A U.K. official, also granted anonymity to speak about the ongoing talks, told POLITICO: “We are trying to find a solution” and “being flexible in our approach.”

SAFE is meant to kick-start a European security renaissance, provide independence from the U.S. and give the continent the tools to defend itself against Russian aggression.

The EU wants the U.K., with its large defense industry, in the tent. Britain wants in too — predicting benefits for its industry and its security. But so far, they’ve not been able to agree about cash.

London has balked at the high price tag Brussels is demanding — ranging from €2 billion to €6.5 billion, but London is offering much less.

While details on the alternative models being discussed are still sketchy, one idea is that the U.K. may be able to avoid the ‘sticker shock’ of a high upfront price by signing up to a more ‘pay as you go’ approach that depends on the ultimate level of U.K. participation.

It might just be what’s needed to get an agreement over the line. Both sides want a deal by Sunday so that the U.K. is in the room before EU member countries submit their spending plans to the Commission on the same day.

Under SAFE, outside countries can only account for a maximum of 35 percent of the value of a weapons system, but the U.K. is negotiating for a higher percentage.

Canada is negotiating a similar agreement.

A European Commission spokesperson said: “As a partner country, and in line with the SAFE regulation, the UK will contribute financially to take part in SAFE, in addition to an administrative fee. That contribution will reflect the benefits the UK gains from its participation.”

A U.K. government spokesperson said the talks “are ongoing,” adding: “The UK is committed to a broad and constructive relationship with the EU, and we are working to implement the package agreed at the UK-EU summit in May.”

‘We’re in the concluding phase’

The Commission had previously suggested an earlier deadline last week to give member states time to adjust to possible U.K. membership, but London didn’t play ball.

Two EU diplomats said the Commission had in recent days started sounding “more hopeful” in its briefings to ambassadors in Brussels, signalling a possible “shifting of gears.”

London is hopeful, too. “We think we’re in a concluding phase, working towards Sunday deadline,” the U.K. official quoted above added.

Still, the timeline could in theory flex further.

One EU diplomat suggested member countries could always tweak their bids after the terms of U.K. participation become clear, even beyond Sunday. “It isn’t ideal,” but could still work, they added.

However, the diplomats added that the Commission has consistently made clear in its messaging that SAFE could go ahead without the U.K. if there is no deal.

But that outcome is one most in Brussels and London want to avoid. “It’s important for the narrative and future security cooperation — where do you go from here if working with U.K. on defense falls at the first hurdle?” one of the two EU diplomats added.

Jacopo Barigazzi also contributed to this report.

Update: This article has been updated to include responses from the European Commission and U.K. government.