Sorry but that 500 meters is beyond most bluetooth devices. Yes you might jury rig a base station or such but the device you try to talk to can't respond.
Maybe you need to reveal more since the bluetooth speed is far too slow for video files.
I am looking to buy a bluetooth device that can be connected to a desktop computer and used to send out text messages and multimedia to cell phones within a range of 500 meters or more. I am not familiar with this type of technology, so I'm not sure what type of device I need to purchase or where I could purchase it. Any recommendations would be greatly appreciated.