Is there a way to use my iPhone 5's unlimited data on my iPad mini Wi-Fi without the expensive hotspot option? I am grand-fathered in the AT&amp;T unlimited data.  I sometimes like to stream Netflix, Hulu, etc while on lunch break.  Is there a way to airplay it over to my iPad mini, or do some type of internet sharing without paying the ridiculous data rates for sharing and AT&amp;T?
There have been hacks in the past to enable tethering, but in almost all cases, the carrier can tell what you are doing. I have even heard that people that tethered were individually contacted by AT&amp;T to let them know that the tethering fee would be added if they wished to continue tethering and asked the customers to come in to chat if there were perhaps a misunderstanding.

You'll want to look for an unofficial AirPlay receiver app on the jailbreak side of things since Apple isn't even allowing these for solid commercial sound apps - let alone video apps.

Long term - let's hope enough people push for network neutrality in the US cellular space so that there is one tariff for data based on volume - not how you intend to use that data.