So I don't know if this has been said or not, but the pricing for the EVO 4G has been decided on, both in terms of the phone and the plan, but no one besides the team working on the EVO know, not even my contact in billing R&D.
Also, because Sprint billing does not have a mechanism to charge separately for 4G tethering vs. 4G data on the phone, there is good chance that there will be an extra charge if you want to use 4G of any kind on this phone. The reason 4G doesn't cost extra on a Overdrive is because it is rolled in as tethering cost.