i use a combination of a $20 Tucano Second Skin, and a $10 Ikea Messenger Bag, and i LOVE it. it has just enough storage for what i need, and it was the cheapest solution. additionally, if i dont want to take the bag, i can keep my laptop in the sleeve, and toss it in my backpack. it really makes the most sense to me.
but then again, i'm a poor college student.