Amanda, as always, you put most of us to shame with your enlightening in-depth knowledge of the rodeo circuit. I keep waiting for the day when they make you an on-air announcer at one of the events you attend. 
I am intrigued by what you said above, and had never really thought calf-roping would cost the rider more than it would cost them to ride bulls. I always presumed that the horse had a proper owner (stock contractor, as you called it), and stable and all the care it needed, and the calf-roper just spent time training it from when it was young, and then riding it when there was an event. Then again, I always presumed, that if the calf-roper/rider won an event, that he/she would split the winnings with the owner. I don't know where I got these notions, but I'm curious now -- is it not done like that? Please enlighten us some more when you get a chance!
Heya,
Well, as far as I understand to be a calf roper you need to train with your one particular horse for a long time so that you and the horse are working in perfect timing together. It's not the kind of human-animal communication/rhythm that could be transfered very easily by switching horses a lot. In team calf-roping it's even more intricate because two people need to have similarly trained horses and the timing/rhythm between the two people as well as between the people and the horses. It seems possible that a scenario could come up where a calf roper simply works with and trains one horse owned by a separate stock contractor (as long as the rider and the individual horse were well acquainted with each other I'd think that would be enough). But, my bet is that it simply is easier or maybe more common to own your own horse (even it this option would be much more expensive).
In bull riding, the bull is meant to be a "surprise" or an unfamiliar animal to the rider. That's the challenge in bull riding... every bull is different (has different moves, spins different directions, kicks high, kicks low, etc.) and the rider needs to adjust to all those differences with each new ride. A bull rider would certainly never need to own a bull in order to participate in the rodeo circuit whereas a calf roper needs to own the animal they use.
So, it's sort of the opposite in calf roping, where it's pretty much essential to have the horse be the same and familiar. The horse in calf roping wouldn't be "rough stock" or a wild horse... It would be a tame, trained horse.
Other horse events, like saddlebronc riding and bareback riding would involve a "rough stock" (or nearly wild/ untrained horse) and those horses could be owned by a separate stock contractor. I assume that the element of surprise/change animal to animal is part of the challenge in those horse events, much like bull riding.
