Mike Gibbs, who chairs the non-profit Avonlea Resthome Trust, said the amount owed represented half of its budgeted operating surplus that would have been used to upgrade the facilities.
Asked if he had any idea of who could meet the bill he said; "none whatsoever''.
"I wouldn't be at all surprised if we had to wear it.''
Mrs Moore arrived in New Zealand in September 2000, having sold all her possessions in the UK, and was granted a visitor visa that expired in March 2001.
Living at her son's Tokirima farm she overstayed her visa by 10 years and eight months.
With multiple health issues, she moved into Avonlea last year after her son suffered a brain tumour and his chicken farm business was liquidated.
But her stay there has seen her accumulate an enormous bill.
The rest home trust sent her a letter on December 19 telling her she would have to leave the home unless the arrears were paid.
Mr Moore said the matter had been complicated by his mother seeking permanent residency which could take months, "possibly even a couple of years'', to resolve.
Mrs Moore applied for residency under the Family Parent Category on 1 May 2012 but this was not accepted because she failed to meet its requirements.
A subsequent application the next month also failed.
Mr Moore defended his mother coming to New Zealand, saying she had nowhere else to live.
"She was able to come here at her own expense and basically lived here at her own expense on the farm,'' he said.
"People have said she has never paid tax, but on the other hand she has never claimed anything in this country.''
"If someone could come up with a good alternative we would pay but she's not able to live on her own ... and it's physically impossible for her to live at our house.''
Waikato DHB communications manager Mary Anne Gill said a disability support link assessment to ascertain whether Mrs Moore is eligible for rest home care was under way.
If successful, the disability support would meet Mrs Moore's rest home costs.
Immigration New Zealand spokeswoman Rachel Purdom said the department had not received any further applications on her behalf since Mrs Moore's failed family parent residency in June 2012.
She said Mrs Moore was granted a 12-month visitor visa in September after a successful humanitarian appeal to the Immigration and Protection Tribunal.