Unless you live somewhere hot, a coat is your best friend when the temperature lowers. What style do you prefer? Is it a menswear inspired coat, a cozy oversized coat or a trendy duster?
If you're not planning on spending much, this J.o.a. Coat will fit the bill. It's a fail-safe choice, while not very expensive. It is also worth taking a look at this Nasty Gal Coat. It's an item you're bound to love which also doesn't cost too much.