ATH-M50X have served me well. Audio Technica is a good brand but tbh they're not very fashionable (they just look a bit generic) if you care about that.
They're also close backed which I'm beginning to realize I don't like, especially since I have a room to myself again and don't have to worry about sound bleeding.
the ATH-AD700x (which I have) would be the open-back equivalent in terms of price range
but if he needs them to be under $100, the 500x would be a step lower