I have a t-mobile gateway with no cap. My phone is t-mobile so I pay $30 a month (no taxes/extras) for it. I believe if it’s your only thing you want from t-mobile it’s $50 a month.
At least in my area the speeds are plenty fast, ping is around 45, and I think I’ve lost connection that I noticed a couple times in the last year, and not for very long. A lot more consistent connection than my cable internet was.
I suggest having t-mobile send you their gateway and trying it. It’s no charge if you decide you don’t want it within the first two weeks and it’s just month to month billing so no contract bullshit.