I myself am having to deal with a similar issue. I got my horse almost 3 weeks ago. She is a 16.1hh APHA mare. She just turned 10 in February and was stall kept her entire life...I honestly don't think she was ever turned out. SHe was used as her owners trail horse, which is why I bought her. I brought her to my barn 3 weeks ago where she is turned out all the time, with exception of morning and night. She doesn't have the best conformation and she has poor feet which require shoes (but I knew this). I had the vet come yesterday bc my farrier came out again and noticed she was stiff in moving and just didn't move right. Turns out she has fetlock effusions (mild in front, moderate in the back) and her left hock as well. The vet said it is very possible she has arthritis. I am giving her bute paste 2x a day for the next 4 days to reduce the inflammation and am starting her on Cosequin as soon as I can get it. I myself am in college so the added cost of having an arthritic horse is definitely making me think twice about keeping her. Her owner was very defensive when I asked if she could take her back so I have no hope of that. I have listed her for sale, but in the meantime I have already paid for April board so I am going to try and get a handle on her pain/condition in the next 30days with a loading dose of Cosequin.....fingers crossed...I'd hate for it to get any more expensive than that as I just can't afford it.
Good luck to you! I hope everything works out for you! I think both of us have definitely gotten into situations that are far less than ideal at this point in our lives.