'04 to '08 full = $2,800.
'04 to '07 full = $1,800 + '08 subscription ($400) = $2,200.
when you upgrade your licenses, they differ in price depending on the version. but that's why they allow the subscription, which basically is a 12 month pad so you don't get screwed with spending all that money and not getting the latest, when it was like a month apart or something.
as far as where to go, just go to AutoDesk.com and type in some info under the "locate a dealer" section, then they'll give you some phone numbers of some places you can purchase from.
PS: soon as you locate a dealer, they'll give you the dead-on price for upgrades... just gotta check with them.