It depends on the model. At homedepot.com prices range from $138
to $248.
http://www.homedepot.com/webapp/wcs/stores/servlet/Search?keyword=liftmaster&langId=-1&storeId=10051&catalogId=10053
They come in different sizes, it depends on what kind you are
looking for. Here are some to look at.
http://www.homedepot.com/h_d1/N-5yc1vZbrkw/h_d2/Navigation?langId=-1&storeId=10051&catalogId=10053