Amanda Bynes -- Stability Comes at a HIGH Price

Amanda Bynes is ensconced at the UCLA Medical Center -- where she'll be for at least 60 days and worst case scenario a full year. And guess what it costs ... $3,500 a day.

Sources involved with Amanda's treatment tell TMZ ... the cost is so high because it covers not just treatment, but living expenses as well. To put this in perspective, you can get a deluxe executive suite at the Four Seasons Hotel in nearby Beverly Hills for $815 a night.

TMZ broke the story ... a judge ruled on Friday that doctors could keep Amanda on a long-term hold for up to a year, although the goal is 60 days ... after which she'd go home to her mom.

Now for some lump sums. 60 days at UCLA Med Center will cost $210,000. A full year would cost $1,277,500. As for Amanda's insurance, she's a member of SAG but we're told the policy will only cover a small portion of the cost.