Which carrier would y'all recommend for someone that has wifi at home and at work?

I've had T-Mobile for about 12 years and the notion of switching carriers was something I hadn't really considered. I was unemployed for like 2 months earlier this year, and couldn't pay the phone bill during that time. I owed ~400 and was about to pay that this past Friday, but that quickly changed seeing the price hike. So I'm just going to abandon the account.

I have a spare iPhone so I don't mind just letting my current one turn into a brick. Any phone company that's cheap and bare bones? I'm talking about just enough data to listen to music on the way to work.

tl;dr: Abandoning my T-Mobile account and sticking them with the bill. Any cheap phone plan?