Amazon France has listed the Xbox One for €599.99, most likely as a placeholder. Microsoft has yet to officially announce what their next-gen system will cost when it launches later this year. Amazon Germany has also listed Xbox One for €599.99.
It's notable that the PS4 is also down as €599.99 and Sony have also not yet revealed the price of their console. Given the entertainment focus of the Xbox One if such a price is accurate Microsoft will likely have a hard time selling the system on that basis to the mass market, at least until a price cut is introduced.
Noted Microsoft tech blogger and journalist Paul Thurrott has previously commented that the Xbox One "will be expensive" and will cost $499.99. According to Thurrott's sources plans for a $299.99 subscription Xbox One have been scrapped by Microsoft, of course, Thurrott also said Illumiroom would be present at the Xbox One's announcement event, it was not.
One point to take into consideration is that if the next-gen consoles are €599.99 (or €499.99) they'll likely be $599.99 ($499.99) as well despite the currency exchange differences. Prices for Europe include associated sales taxes while US prices do not.
Both the Xbox One and PlayStation 4 are set to be released later this year and we should have a firmer idea of their launch windows after E3 next month. Amazon simply states that the Xbox One will be "available soon".