How many features do you need for it?
Are you just trying to figure out how many revs you're turning? There's a small tach on ebay for about $25. It only has 2 leads, one goes to ground and the other wraps around the ignition wire
It functions as a real time tachometer and an elapsed hour meter.
If you're craving more features, you might take a look at a trail tech setup. They have a bunch more features but the setup will run you considerably more than $25.