Is there an app that will provide hdmi output at the micro usb port? I have unlimited data on my phone, but if i tether using my phone as a mobile hot spot, I'm limited to 5gigs per month.
Nope, the device has to have MHL or Slimport capability built-in. Chromecast uses your home wi-fi network, not your mobile network, so your mobile data limit wouldn't be affected.