So I seen a thread the other day with this method, tried it and it still works in story mode to get unlimited money after patch. I made a video which you can see here: https://www.youtube.com/watch?v=DR4IJJisyE0

Firstly, be aware the better the horse you have the more money you are going to make with this glitch. So if you have a Rose Grey Arabian fully bonded you are going to make $375 each time you sell the horse. If you have a white Arabian fully bonded you are going to be able to sell it for $350 and so on.

To do this glitch follow the steps:

• Call your horse and make your way to the Horse Fence just on the outside of Rhodes (see here for location)
• Once there, set up a camp nearby and go to sleep for any amount of time
• When awake, make a manual save and then exit the game from inside the menu
• When fully exitied from the game, load story mode back up. If it doesn't load up the save you just made, manually load it up from the load menu.
• Once fully loaded, call your horse and make your way back to the fence. Now sell your horse to the fence and once sold, your horse will respawn behind you allowing you to sell the horse as many times as you like. Your horse will respawn right behind you every time you sell it, allowing you to sell it again straight away.
• Once you've got all the money you like, make a save and that's it.