Grad student looking to buy a suit, need some suggestions

First step is to go to the stores you'd be interested in purchasing suits from and figure out the suit models that fit you best. THEN start perusing eBay...otherwise you'll have a lot more miss than hit.
 

With the huge drop, you should look at suit separates, so that you can get both the jacket and trousers to fit. Even then you will probably require some tailoring to take in the waist, so allow for this in your budget. Jos. A Bank does not get a lot of love around here, but it seems their biggest issues are how poorly their stuff fits the average person and how bad theirs salesmen are. You may be a good fit in their stuff, though. I suggest just trying them out and see how they fit. Tommy Hilfiger also makes a reasonable selection of suit separates, you can find these in many department stores.

He said jean sizes. Factor in vanity sizing and all the other issues and while the drop is higher then average he might be "only" 8inch or so.

J. Crew Ludlow, perhaps? Available on the internet at a fairly reasonable price. SuitSupply is also good value for money, I hear.

Yeah... sale season, so you may well find something at the mall. Especially given your height and shape, you don't want to go ebay without the try on...

You mean Tallia from Men's Wearhouse? AVOID. Jos. A. Bank probably would look too bulky on a young person with broad shoulders and a large drop. The missing piece of information here is geographic location. The course of action should include being measured by an expert, trying on before buying, and probably a moderate amount of tailoring afterward.