Wholesale bandwidth cost

What’s the ballpark cost per GB nowadays for large quantities of bandwidth, say for file hosting, assuming one was looking to buy several thousand GB/month?

I know that you just can’t extrapolate from the cheap consumer plans that offer a lot of bandwidth, because those are based on the assumption that 90%+ of the consumers use <10% of their bandwidth. So I’m looking for the cost that a major commercial site would likely pay. (No, it’s not so much for myself, as that I’m trying to estimate the cost structure of some other folks out there…)

For very high bandwidth you don’t go metered anymore – you typically go to an unmetered fixed bandwidth connection such as 10Mbps or 100Mbps (and all in between). For prices on those check out colo facility quotes from places like Capital Internet, SiteSouth, RackSpace, etc.

Yeah, I would imagine the big(ger) boys use dedicated lines, paid by the month. Still, you can’t just say that a 1MB connection = 1 * 60 seconds * 60 minutes * 24 hours * 30 days = 2592 GB/month, because your customers are using that most heavily at certain hours, so the effective, useable monthly bandwidth through which your customers can download would be much less - perhaps a third of that. That makes it hard to say that a 10MB download costs a provider XX cents.

But I know that some sites sell peak overflow bandwidth, which might be priced by the absolute GB, rather than as an always available 1MB or whatever. Does anyone know what such ‘overflow’ bandwidth costs, or maybe, factoring in consumer usage patterns, what a big site computes it’s cost per MB for downloads at (for internal accounting)?