Heads up, NEVER skimp on a power supply. Cheap ones are just liable to give either far less power than they claim and just cause your PC to shut down or just deliver a huge power surge that fries your computer. The extra money for a branded power supply with an 80+ certification is worth it and HIGHLY advisable.

And no, apple hardware isn't expensive because of scarcity, infact price per unit to manufacture is infact far lower than many other companies hit but then thats probably because they produce an abnormal amount from a single plant rather than smaller amounts from several plants and use what is borderline slavery (even children). They can afford to sell them cheaper. Its just designer gear so they sell it for more (some people say they look nicer, thats not worth a 400% price markup IMO).

You didn't mention a GPU or hard disk btw. I assume you didn't leave them out. If you ask your school you may be able to get a discount on buying a windows 7 CD.

I also recommend linux mint over ubunut, it has a far better list of default installed software. Ubunut can't play DVD's for example as the codecs aren't installed, they are in mint. Mint is based on ubuntu so software for ubuntu specifically will work in mint.