How much would the ps5 or xbox x series cost?

Ps5 400 euro and xbox x 500 euro? Is this realistic?

Both consoles will probably cost 500 euro. 400 euro would be really little. If the PS5 will have the same specs as the Xbox Series X, it won't be really cheaper.

The xbox is supposed to be a bit stronger than the ps as always!

Related to the teraflops, yes. But it will have to be seen how this will affect the games in the end.

Do you think the new xbox could even cost 600 euro?

No, at least not the normal variant. Maybe there will be an even stronger version of it someday. At first I don't think it will cost more than 500 euro.