Maybe you don't need the latest and greatest technology when it comes to your third or fourth screen, and if you can save a little money, why not? The LTE-equipped Samsung Galaxy Tab 3 is on sale right now for $99, and it's unlocked to work on T-Mobile or AT&T.
The Tab 3 is a modestly specced tablet with a 7-inch 1024x600 LCD, 1.5GB of RAM, and a 1.7GHz dual-core CPU. It's not amazing, but it's only $99 for an LTE tablet.
This is the T-Mobile model, but it should have bands for at least part of AT&T's network too. The specs list Android 4.2, but that's just what it shipped with. There should be a KitKat update available. It ships free in the US with tax only in New Jersey.