MBL Site
There are 3 types of  cable lifts.   The overhead cable lift, dockside cable lift and the free standing cable lift.

It is Muskoka BoatlIfts opinion that the overhead cable lift is the best  valued lift.  Its versatality and cost make it hard to beat.   Typically the overhead lift will be installed in a boathouse or boatport.  It needs the building structure to hold the  boat weight.  The typical overhead cable lift mounted in a boathouse is in the $5700 area (installed).
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The dockside  cable boat lift for small boats and jet skis can be found in the jet ski tabMuskoka Boatlifts  does not sell a dockside cable lift for large boats.  We would refer you to  Viking Boatlifts in Oakville www.vikingboatlift.com/photos.html.  It is our understanding that you would be in the $8500 plus range for this kind of  lift (20ft boat )..  You need to contact Viking for  pricing.  Deep water and winter boat storage can be accomodated by this lift.

Free standing cable lifts have an aluminium structure in the water to lift the boat.   They typically need to be removed from the water for the winter which can make them burdensome.  They are available with a manual or electric winch    The price range is broad.  A lift that can handle a 20ft boat with an electric winch would be  $7900 installed while a manual winch fixed leg lift would be $4400 (17ft boat).  Water depth 12" to 66".
http://www.naylorsystems.com/Aluminum%20lifts/Aluminum%20Lifts.html
MUSKOKA  BOATLIFTS:  Cable