East Berkshire is due to be left without mental health in-patient services in a bid to save money.
It would mean patients from Slough and Maidenhead having to travel up to 20 miles for beds at Reading's purpose-built Prospect Park Hospital.
Three ideas were consulted on but the NHS trust said a plan to build a new facility in Slough was too expensive.
It also said a proposal to keep some services in Maidenhead was not supported by clinicians.
Berkshire Healthcare NHS Foundation Trust currently provides hospital care from three sites in east Berkshire - Wexham Park in Slough, St Mark's in Maidenhead and Heatherwood in Ascot.
Two of the three options involve moving all or the majority of in-patients to Prospect Park while the third is to build a new mental health unit in Slough.
A final decision will be made by Berkshire Healthcare NHS Foundation Trust and NHS Berkshire East in June.
In a joint statement they said: "Both boards understand the unaffordability of option three [new Slough facility] in the current and future economic environment.
"Option two [keeping some services in Maidenhead] is not supported by the clinicians."
The boards said this option would mean older people being cared for in the wrong environment, because it combined patients with unexplained disorders with those whose illnesses could be explained.
This would "not be conducive to high quality care", the clinicians added.
The trust, which is trying to save £12m over the next three years, said it was working on a plan to put aside £100,000 a year for travel costs.
Theresa May, MP for Maidenhead, said: "I have always said that it would be unacceptable for vital mental health services for older people to be moved to Reading, leaving Maidenhead residents with no local facilities.
"There are still a few months until a final decision is reached and I will continue putting the case for St Mark's."
Peter Wilson, whose son Ross has spent time in Heatherwood Hospital, said: "[Moving in-patient services] would have a huge impact because we saw him every day in hospital for a couple of months and that was about 20 minutes to Ascot.
"To Prospect Park that's an hour or more, it would have made an enormous difference to travelling.
"I think [with] people who suffer breakdowns, you would swap a mass amount of facilities just for the company of your loved ones."