No there isn' a 600 class anymore, a few years ago there was.
Have you got experience in an national endurance series? Very important to compete in this sort of race class, you will learn a lot of that.
Overhere in Belgium you got two endurance series , one only races at zolder the other also race at Brno , Spa, Magny cours and Hockenheim 4H races.
this is a kinda low budget type of race class .
The moment you enter the world endurance the costs are much higher of course because of the away missions
You can enter the superstock class, but a real stock bike wouldn't stand a change it needs to be blue printed in order to compete in the class ,and that is also a considerable lot of nero's.