My sharer pays for half of everything, which works out at £40 per month, unless he's had any extras like new shoes or vet etc.
She gets him 3 days a week and has no chores to do because he lives out all year anyway. All she has to do is make sure he is fed and happy on her days, then she has...
If the pony is that ill it would be so cruel to unsettle her by moving her. Especially if you think she'd only get passed around.
If you can't keep her, being in the state she's in I'd PTS. Moving her around will more than likely make her even worse, it's not fair to put her through that.