That's true, they're overselling by shedloads to give you that amount of data transfer! Most servers in DC's only come with 1-2000gb data transfer altogether for at least $80 per month. They'd need to oversell their bandwidth by at least 2.5x times to break even, and that's presuming they have no other costs.
And unless they're managing their overselling really well, avoid them like the plague!
Thats a good deal. If i were you, since they are popular, try them out for a month and see how the service / support is. If you are satisfied, then youv'e found a great host. If not, time to look at other ones.
__________________ Chris Willson