make a whole presentation and make it really serious and how you can work out any money problems and how you can take care of it. put in every little detail of owning a horse. put in all expenses. any question they could possibly have you have to have an answer to it. also maybe try to work at the barn or find a way to show your committed! hope this helped!!!
Make sure the owner is 100% selling him and is completely positive this is the right thing to do. They may be putting him up for sale because they think you will buy him. Make sure they know that you can’t buy him but would love to still lease him. At this point if they were only selling him to see if you would buy him then they may change their mind. But, if they are still selling him see if anyone near you needs a horse. Look for other riders at your barn, friends, or neighbors. If someone near you buys him you may be able to lease him from them. Unfortunately there isn’t much you can do other than try and convince your trainer not to sell or your parents to buy. Hope this helps and hopefully everything works out for you!