Would be interested to know where you saw an xbox360 sell for US$1 million. Perhaps you meant $1,000?
While fuzzba11's pessimism may be annoying, or a wet blanket on your enthusiasm, I believe he is making a valid point. Specifically, what is the point of this project? You are not giving many details so that this very enthusiastic community can offer advice.
For example:
Are you only doing this to show how powerful a computer today can be?
Are you going to be modding the case to make it truely eye catching?
If so, what kind of mods are you wanting to do? integrated lcds, integrated water cooling?
If you can get the school to loan the money (I call it a loan since your goal seems to be to repay it), great, I for one look forward to seeing pics of the results. However, if you are asking your school to put out this kind of money just to build a "wet dream specs" comp, I would point out that many of the individuals on this board who get great speeds will often spend months tweeking and tuning to get the absolute best out of their system. in this time, new items will often come out, lowering the value of the original material.
Of course, if this is to be a true PR build, showing what the students of this school are doing, would it not be better to truely put your skills to the forefront and go full custom, with as little "off the shelf" hardware as possible? Perhaps integrate multiple classes into the project, and create a "Digital Mascot" as it were?
I do wish you luck, and it seems you have a solid foundation of what the bleeding edge is in the realm of computers. If you are able to pursue this project, I have no doubt that the community here can be a priceless resource to aid you.
Take care,
JKrepps