The cost of installation will be directly related to the cost of living in your area. If you go through one of the large home improvement stores to buy the disposal, you can likely add installation for $50-$100. If you bring in a plumber to install it, expect to pay an hourly rate, depending on what's involved. If you have a disposal and simply need to replace it, you can likely do the installation yourself. For a new disposal plus installation, expect to pay $200 - $500, depending on your location, the unit you choose, and whether the wiring is in place.