This isn't another "how can i convince my parents" question?

I would try to save up so that you can pay the difference. If he's willing to pay 3000 dollars can you pay the extra 1000? And if he'll pay 200 a month can you work off the extra 90 plus the money for the farrier etcetera. If you can, great, go for it. If you can't, I'm sorry but I think you will have to let this one go. Other horses will turn up