I'm actually in the exact same situation, needing a laptop for my computer class labs. This is my first class, and I need to run windows. So I have considered buying a cheap laptop loaded with windows for now and wait for macbook pro retina release hopefully by summer. But at some point I need something with a cpu that can handle a larger monitor, so that would mean buying windows for my mb pro, because the cheap laptop might not be able to handle the large monitor from what I understand. Plus, by cheap I still seem to be looking at around $280 to $400.
So I am pretty set on buying the low end 13" MB Pro Retina for now, though Best Buy does have a sale on a few higher end configurations this week.
My thought was, I could buy a low end MB Pro now, or a high end 15" at twice the price with the idea it might last twice as long. But with the money I save on the lowed `13", I could buy another low end in a couple of years that might be better than the high end 15" I buy now. At least my reasoning is running somewhere along those lines, however fallible and speculative it may be.