I've paid anywhere from 50$ (yes, 50$)-300$, put 30-60 days on the horse, and resold for 600-1000$. That was when I didn't have to worry about board costs, as I used my parents fields, and facilities, so virtually costed me nothing to train the horse. I really haven't bought and sold any horses in the past few years, but have rather spent more time training others horses. That usually brings atleast 300$ per horse, or if I work one on one with a horse and handler, 30-60$ per training session, usually at the owner's place.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."