As I already have 5.5 there is no need to upgrade from 5.0. So where can I buy this price-reduced upgrade??
TRADOS 6.0 includes everything that was in the TRADOS 5.5 "Power Pack" (Multiterm iX for terminology management, T-Windows for translating in Excel, etc., and the XML validator), plus some changes to the interface, and support for compatibility with the TRADOS TM Server.
If you have 5.5, the upgrade is just 55$/euro. If you are trying to decide which to buy, there would be no reason to buy 5.5 new. If you buy 5.5 used, you will want to upgrade (so just do the math--your price for 6.0 will be whatever you pay for the used copy, plus 55$/euro.)
By comparison, we are selling TRADOS 6.0 on TGB, new and direct from TRADOS, for $595 right now. http://www.translatorgroupbuying.com