The Friends of the Old Town Hall - which formed the Castlegate Preservation Trust last year - hope to raise thousands of pounds to pay for legal advice before selling shares that would allow members to take over and restore the city's former civic headquarters.
The group hopes to strike a deal that would involve the council compulsorily purchasing the place from owners G1 London Properties Ltd, then handing it over to supporters to create a mixed-use complex featuring workspaces, a café, meeting rooms and a performance venue.
Having previously been listed for sale with an asking price of Â£3 million, in March it emerged the Victorian premises were earmarked for apartments by G1. Built in the 1800s, the site on Waingate was used as a courthouse after the Town Hall moved to Pinstone Street. It later fell into disuse when the combined court centre opened on West Bar.
But Valerie Bayliss, chair of the Friends, said: "We can't see a commercial solution working for that building. Raising the money for the purchase and restoration is going to be a slog but it's the only way to do it. It's all fixable, albeit at a price."
An earlier survey indicated that repairs and refurbishments would cost 'well north of Â£10 million', added Valerie, who also chairs the trust which aims to improve the wider Castlegate area. The 'conservation deficit' - when the cost of fixing a building exceeds its value when repaired - is 'so big that you're not going to get a commercial developer taking it on', she said.
The group held its latest meeting on Monday evening in Neepsend at the Gardeners Rest pub, which was taken over by regulars in 2017 following a similar community share offer. A proposal to turn Portland Works, the former cutlery factory in Highfield, into flats was fended off in the same way.
Valerie said there was a 'very good turnout'. "The room was crowded and we had a lively discussion. We want to do a share offer, but before we announce it we need to raise a bit more cash, so we're looking to crowdfund over the summer and into September to raise about Â£2,000."
The sum will be match-funded by the Power to Change charitable trust, generating up to Â£8,000 that would be used to pay for legal advice on the shares.
The Friends have an important meeting lined up with the council next month, after which the appeal will start. The authority, which has set some money aside to carry out essential repairs to the Old Town Hall, has been trying to gain access to the premises to make an inspection.
"They have got powers and no money, and we haven't got powers but we can try and raise money," said Valerie. "We think there's a deal in there."
G1 put a 'completely unrealistic' price on the site, she continued. "It's worth nothing at the moment."
Rumours persist that the submission of a planning application for flats is imminent. "If they gutted the building and were allowed to punch holes in it you might be able to make it stack up. But then you've lost everything that makes it worth keeping. We wouldn't be keen on that."
A phased restoration would take place if the community takeover is successful, with completion likely in the 2020s. "It takes a long time," said Valerie.
In 2007, the Old Town Hall was named by the Victorian Society as one of its top ten most endangered buildings.