If you're in the market for a gigantic, tablet-like smartphone that doesn't start with the word "Galaxy," you'd be hard-pressed to find a better candidate than the LG Optimus G Pro. And if you want it on AT&T, you won't find anywhere that has it cheaper than Amazon. The 5.5-inch phone is just $49.99 for new contact signees and returning customers whose 2-year re-up has come, with free two-day shipping to boot (you don't even need Amazon Prime). Without a contract, you're looking at a $600 retail price.
The G Pro (as the cool kids are calling it) is LG's current flagship for the American market, with its enormous 5.5-inch 1080p screen taking center stage. A 1.7Ghz Snapdragon 600 processor, 2GB of RAM, 32GB of storage, and a 13 megapixel rear camera don't hurt, either - this is a lot of high-end hardware for fifty bones. This price is fifty bucks less than AT&T's standard retail price, and $20 less than the last time Amazon put the G Pro on sale. There's no telling how long the $50 price will last.
The phone has a sizeable 3140mAh battery, but if you want longevity that's long and strong and down to get the amperage on, ZeroLemon has a gargantuan 9300mAh version with extended battery cover for $45, also on Amazon.
Amazon Wireless: AT&T LG Optimus G Pro