Unless your stalls are huge, you are going to need a bobcat 463, or New Holland LX125, as they measure 44" wide, 36" with the narrow kit and bucket.
Either of these operate relativley similarly, and would do the same job in comparison. We have dug swimming pools with 463's before we changed operating systems, and compared to a basement, the time taken was about a week with 2" on each side of the machine traveling in and out to the dump truck. That should give you a good gauge to compare from. At your $7,500.00 budget, you can find some fairly low hour machines in that class in that range.
Now, if your stalls are bigger, you could run a 763 bobcat or the NH LX170.
Personally, I would steer to Bobcat if that was one of my two choices, New Hollands in the larger models are cumbersome, which means you will have a hell of a time in the tight confines of horse stalls, under powered, and can't dig their way out of loose soils let alone on hills or hard soils. If that is what you end up with just get some cheese and it will go well with the drive motor whines.... The multiple knuckle and hinges wear fast, and the boom becomes so unstable you need to rely on the rub rails on the cab to keep the boom straight. I watched one on flat level ground go on it's side when the operator had a concrete barrier on the forks about 3 feet up and the weight threw it right over. They can however, lift a house.
The Bobcat is designed more for excavation, even though it relies on yank em sticks and pedals to control the machine. It will turn tighter and be more suitable for horse stalls.
