I'm moving to Pittsburgh, PA for graduate school, and want to commute to school when the weather is good via bike. I am completely new to riding, aside from recreationally, and I have no idea what type/brand or anything to buy. I'm looking to spend 300-400 dollars, but I don't even know if that is realistic or not for what I'm looking for. I need it to be very lightweight, as I will have to carry it up and down flights of stairs in the city. Any and all information would be incredibly helpful! Thanks!