GoKawiilIf you want a phone that works on the major US carriers out of the box without any big surprises, you might want to keep your expectations in check. At $100 or less, you're looking at something that's about as basic as it gets.
Probably the best option in this category is the Motorola's 2024 Moto G Play, often discounted from its $150 list price to $100. It has a big 6.5-inch HD+ screen at 90Hz, a 50-megapixel main camera, 64GB of storage with a microSD card slot and 4GB of RAM. Its 5,000mAh battery should at least get you through the day, and its mostly stock Android experience is a plus. The catch is that it maxes out at 4G LTE speeds.
That spec sheet is nothing to get excited about. (That is, unless you're a time-traveling smartphone enthusiast from 2012.) But it does the job well enough for people who just want the bare minimum.
The TCL 30 Z is unlocked and advertised as compatible with the major carriers, but it's a turd of a phone. You get a 6.1-inch HD display, a smaller 3,000mAh battery, 32GB of storage, 3GB of RAM, a rudimentary 8-megapixel rear camera and 4G LTE. On the bright side, an "Amazon Renewed" model costs only about $61. Brands like BLU also sell new unlocked phones below $100, but they come with rock-bottom specs and limited carrier compatibility.
That's about as good as the fully unlocked options get. What you're paying for here is freedom from restrictions, not a phone you'll likely enjoy.