That's odd - every datacenter (read: colocation facility) I've worked with had clear pricing for rack space, power, bandwidth, etc -I could use as much as I wan

That's odd - every datacenter (read: colocation facility) I've worked with had clear pricing for rack space, power, bandwidth, etc -I could use as much as I wanted, and I knew what I'd pay for it, and would re-negotiate if the regular usage was going to go higher. By DC's - do you mean some kind of web-hosting provider instead? Even the VM providers I use all have soft & hard limits on traffic stated clearly - in practice, anyone offering "unlimited" anything is automatically excluded from any kind of critical business hosting decision - because that's not realistic or maintainable.