Put it this way.. Back in 98-99 when I was doing consulting SEO work on the side for this one big firm, ebay was a client and spending over $20M a month back then, and they had just about every keyword you could ever imagine. I mean the lists were fucking massive. Gigs full of excel files of keywords, because back then, there were no API's for kw's to make the life of an SEO/SEM easier, so most of the shit you had to do was by hand submissions, not to mention they were buying the entire keywords for MSN.com at the time as well. Money is of no object with them, and why should it be, I mean, their overhead is fucking tiny compared to what they make.
My guess is ebay is spending over $4M a day at least. They bid on every fucking keyword under the sun on adsense and adwords, on YSM and YPN, and on MSN, and on every small PPC engine and all of the price comparison engines. That's a lot of fucking money to be spending everyday for 365 days a year for YEARS straight already.