Lines like that are usually used by big companies who want to be able to send an assload of data real fast. I don't know the exact cost, but I've seen figures before, and, if I remember correctly, it's in the hundreds and even thousands per month.
I remember doing a job shadow at some power backbone with their Network Administrator. They had a shared DS3 line he told me it ran them about $1400 a month. That's not even for the whole line, either. Crazy stuff.
Now if you wanted some real speed, start looking at OC lines. Something around OC768 outta do ya