OK so I just installed the "20 Dollar" tach from fleabay on my bike and I am pleased to say it works great! I had a problem in the beginning as it kept resetting itself but after unwrapping it a few time from the spark plug wire it started working perfectly. I used a reflector mount on the handlebars and have the meter mounted over my handlebar clamp.
is the tach I bought (Its at 10% off so hurry fast! lol). If you are interested in adding a tacho on the cheap on your bike I would DEFINITELY recommend this one
P.S. I have my tach wire wrapped around about 3 1/2 times. That seems to be the perfect number