Firstly, where in the world are you? If you are in the EU, then consumer law covers you for up to 6 years as long as it is reasonably a manufacturing defect. So, if you have not abused it, you may have a good case.
If not, I would still take it to an Apple store, and ask them to look at it, which I think is free. It is still a relatively new computer, and I don't think it unreasonable for them to fix it for a small charge, or take pity (read: he/she was nice to us and could have been a jerk and threatened to sue us) on you and do it for free. It's amazing what being nice and calm and clearly explaining the dilemma can do for you. And if that doesn't work, politely ask if you can speak to the manager, rinse and repeat.
And if all that doesn't work, there's always the email to Tim Cook...
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Oh, and if you can check that it's not just the power adapter that has failed. Even the grumpiest of computer store assistants should let you test that one!
