You can buy a tiny "pocket" clipper from Wahl for less than $15 and the darn thing has the disposable battery included. I bought one for desensitizing foals. It works great for whiskers and very fine hair, but it is kind of loud for its size. Alternatively the $30 ones sold for human or pet hair at places like Walmart will also work.
Buying a decent pair of clippers is a good investment. I had my first Oster A-5 for 10+ years before one of my dodo brained dogs knocked it off a bucket while they were rough housing causing the casing to crack. I bought a new two speed A-5 from an online Christmas special for $99 which is basically half price. There are deals to be had if you shop around.
Another thing to remember with a disposable razor is that you can give them razor burn if you aren't careful. Make sure to wash the muzzle well first and use a form of lubrication if needed. Also be extra careful if your horse wiggles when he feels tickled. You will probably need your free hand to help keep areas of skin taught so it might also be nice to have help holding him or distracting/reassuring him with some petting. Posted via Mobile Device