Q&A for How to Buy a Horse in Red Dead Redemption

No particular level, but you can get a horse more cheaply if your fame and honor are high.

Your horse will be in your inventory, and you must select it and whistle for it to come to you.

You may want to reload your last save from before it died. That's what I do.

You could go to other stores, if that doesn't work, you'll have to wait until the time passes a bit then try again. It also may be a glitch. Try going out of the game and coming back in again.