Best inexpensive cell phone that gets excellent reception?

My boyfriend’s current dorm at his school doesn’t get reception on his crappy old cell phone. I’m really tired of not being able to talk to him. I’m buying him a new phone.
Plan can not change. We have AT&T. I would really prefer to spend as little money as possible. Ideally under 100. The phone doesn’t have to have ANY other functions apart from being able to make calls and text message. I care about nothing else.

I really miss being able to talk to him. If there were a more simple solution, I wouldn’t be asking this.