If you don't have a Walgreen's around you (which I don't), you can also buy one from Target. The cheapest one is like $6 or $7. You would need to disable the alarm of this one too.
If you're scared of disabling the alarm yourself, there's one at Radio Shack as well that's like $15, and you can ask the employees there to disable it for you. This is what TM suggested to its students, but another student told me about the Target one, so I got that. The reason Target's is cheaper is that Radio Shack's has a number pad where you can punch in the 35 minutes, whereas with the Target one (and I would imagine with the Walgreen's one too, since it's $4), you have to push the minute button 35 times. BUT, when it reaches 0:00, it automatically resets to 35:00. So you only have to set the time once. Another problem I had with the Target one was that I couldn't figure out how to turn it off, so I had to take out the batteries each time because I didn't want them to die during the test. This meant that every time I put the batteries back in, I had to set the time again. I think it's worth doing that to save $10 though.
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