1 Professional installation of a garbage disposal might cost $100 to $500 or more depending on the complexity of the job. 2  Replacing an existing disposal is cheaper than a brand new installation. 3  Adding a new electrical switch will cost more than plumbing alone. Garbage disposals can cost under $100 and more than $600, although you’ll find many good quality units priced between $150 and $350. 2  Higher-priced units have larger motors, more options, and stainless steel components. 3  Those at the top of the price spectrum are foodservice-grade.