soooo, it seems that last mile forms a major portion of the costs and thats why we(consumers) end up paying telcos a lot!!!
I should probably clarify: it forms a major portion of the costs of the BUILDING of a network. Since the lifespan of a last mile network is typically expected to range from 20 years (Aerial cables) to about 30 or 35 years (buried), the monthly cost of those cables can work out to be fairly minimal. Keeping in mind, I'm also talking about my case which involves primarily fiber optics, not copper.
Aerial cabling is of course cheaper to run, and can just be added to existing power & phone poles, whereas buried fiber can run in to costing crores per kilometer (in Mumbai, at least) due to directional drilling and whatnot. But once it's in, it's in, and there are rarely too many more additional costs, and so the RoI for the network doesn't usually exceed something like 5 years (of course, this varies according to the "cost per premises passed" which differs by country, state, city, suburb and even street).
This is why/how we're offering the "Hayai Zone" as well as a bunch of caching and mirrors: since, like all ISPs, the available International Bandwidth capacity is quite limited compared to what we can have internally, we figure that since it's there, you might as well use it.
If I had to guess, I would say that the cost per GB inside our network works out to be not more than a few paise, whereas as I've described in other threads, the international segment works out to well over Rs15/GB, so this part is the part we care about measuring.
The way we work this out is, despite the fact that we buy bandwidth in increments of 155mbit/s, we can still transfer a limited number of GB in every month based on that speed, so we work out the cost per GB by saying that for every 155mbit/s we buy, we can transfer somewhere in the vicinity of 45Tbytes or 46080Gbytes: round that down to 90% usage or 40Tbytes or 40960Gbytes, then take our price
of course if you are still working on launching in india 
