I do think you can do this, if you have the skills to turn horses into calm, safe horses AND you consider that you are using the horse to ride and learn on.
I myself have spent a lifetime buying other's rejects and turning them into safe horses.
Many were rearers, as this terrifies most people. Others were manhandled, and just needed a little TLC and tenderness.
I didn't do this to make a profit though, I did it because I wanted a horse to ride and I have never had enough money to buy the caliber of horse I wanted, so I had to train them to it.
To train a horse, especially spoiled horses, enough that they do not revert back to bad habits will take (on average) 6-12 months IMO. So plan to keep the horse about a year.
Horses are cheaper in fall, so that is when I would usually buy one, then work them over the winter and early spring do some shows. Then decide if I wanted to sell or keep them.
If you wanted to help horses to a better future, by giving them skills, trust in humans, and willingness to work; you will have personal satisfaction, and hopefully at least break even.
Now, much older, I just keep my horses, and don't sell them.
Best wishes! Turn those dreams into a reality