does the lexus nx200t require premium fuel? Could I use another grade of fuel without harming the car?
Premium required. 89 or preferably 91 octane. Yours is a high compression, high quality, well engineered engine. It could pre-detonate on lesser fuel, and yes, harm engine.
Also, from these retailers ONLY - Cheap gas, whatever octane does not have the detergents your car needs. http://www.toptiergas.com/retailers/