You should familiarize yourself with per Mbps billing. Almost every colo provider out there bills using a method called "95th percentile". You will get somewhat varied numbers of how many GB you can transfer per Mbps based on your traffic profile, but it will range from 250 to 320GB or so. You might find a host that specializes in 1 or 2U colocation billing on a GB model, but really you won't find it often in colo.
Generally speaking, colo customers use much closer to the purchased amount of bandwidth and the oversubscription ratio is much, much lower than dedicated server customers.