Performance wise, the money will go farther on a PC than a Mac. Plus the ease of dealing with student documents that are more likely to be PC compatible etc. Everyone I see in my classes with Macs is always struggling to integrate with the university's PC-based system.
I have a 'custom built' (by the manufacturer) 13" Sony Viao that I spent around $1200 in March 2013. It's i7, 12 gb ram, non-integrated graphics, and other non-necessary upgrades. I originally bought it for gaming and schoolwork, but now I mostly do internet/school work/video streaming. It handles everything well. It's super small and light -- I think it weighs around 3 lbs. I can fit it in my (fairly large) purse). I love the convenience factor of that, and it is a pretty powerful laptop especially for its size. Unfortunately I don't think they make them anymore :(
If you go for the top end of the budget, assuming it's 100% covered by your job, and get an actual small laptop, not a netbook or ultrabook or tablet/laptop or whatever else they're making, you should be able to get a strong lightweight PC that has enough hardware to last you a significant amount of time. If I were in your position I'd look around at manufacturer's websites (Dell, Asus, etc) and see if there's a build-your-own type feature where you can maximize performance within your budget.
Also, Apples have metal bodies and heavier than plastic PCs -- the 13" MacBook Pro Air weighs 4 lbs to my Vaio's 2.4 lbs. And they're charging $1099 for an i5; like I said, two years ago I paid $1200 for an i7. Macs are overpriced for their functional components.