Your "Dish" should already get local CBS, ABC, NBC, PBS stations, those are typically located below Dish channels 100.
To recieve your local OTA channel directly, you do not need the Dish system, plug in a antenna DIRECTLY to your TV sets ANTENNA/CABLE coax input.
Once you have the antenna connected, change TV from your Dish input (HDMI, Component or Composite and select Antenna/OTA/Cable from your TVs menu.
Once you on the antenna/cable input you need to do a channel scan.
Once scan has completed you now can watch your local OTA channels.
Yes, it means you must switch between inputs and yes, you will not have DVR capability but you now get all of the local channels plus the sub channels and it didn't cost anything other than the antenna..