Probably not what you want to hear, but my advice is similar to what others have said. I myself am an ID student (3rd year out of 4), so I don't have the time to make a lot of money on the side. I did save up for about 80% of a high end Haswell 15" rMBP. Of course I bought one anyway, with the idea of paying back that last 20% to the "person" that helped me
mom
I had 1,5 month to decide (extended refund period), but after 2 weeks I already knew it: I returned it. The first months of 2014 are going to be a bit unstable/unsure for my girlfriend from a financial point of view, so the need to be prepared to support her, us, was higher then having this product I'm so passionate about. Another thing was the fact that I put myself under stress, financially. I could manage getting around, but it would be tight considering the fact I spend most of my money on such an expensive product.
And in the end, I can manage at least another year without a super powerful 15" rMBP. Of course it would be much nicer to have such a MacBook, but you got to get your priorities straight in life. I know it's VERY hard to do this at the age of 18, I made some stupid decisions myself back then. But try to think clear, ask yourself questions like: do you REALLY need it? Can you delay your purchase? Is that MacBook really going to be worth so much money? What will the
actual difference be between what you have now and that expensive MacBook? Are you willing to pay that much money for the difference?
Good luck!
PS: like somebody else said, either way, you might learn important lessons from whatever you will end up doing.