I purchased a Wahl Human Clipper, intending on using it for bridle paths - it cannot handle the thick hair and doesn't have a fast enough speed in order to clip though it. It works okay for legs and faces, but it leaves lines in the coat and overheats quickly.
Instead, I use an Andis clipper that was marketed for dog and cat grooming. I actually got it for free years ago from a friend when I started grooming school, but it couldn't handle working 8+ hours in a day without overheating. It works wonderfully for the touch ups that I need to do on my horses! It might be worth it to call around to pet grooming shops and see if anyone has one they would like to sell or give away. At the shop I worked at, we had a bucket full of old "back-up" clippers that still worked fine for short periods of time, but simply couldn't handle the stress of running all day long.