Key popped off on keyboard?

My school gave us all laptops, I've had mine three years, little damage other than a few scratches and such from use. Well, today I was typing a report for english and the N key popped off, it still works and I have all the parts besides the little rubber thing that goes under the key. My school will charge me fifty(50) dollars to fix it! Thats a ridiculous amount! I was wondering if I could take it to a repair store and they could fix it? Would it cost more to have it fixed there than the school? How much would it approximately?

Added (1). lenovo thinkpad x131e chromebook 11.6" led intel celeron dual core 1.50ghz model 628323u

What brand of laptop is it? I bought a keyboard for a friend's Dell laptop and the keyboard was $20.00 from Dell. Then it is just a matter of finding an on-line video to show you how to install it.