Pay whatever you want for the €0+ Stories.
Other stories that cost more are early access which aren't fully uploaded to Deviantart yet. (DA: deviantart.com/reiko-samaa)
And of course don't share early access stories until they're fully uploaded please.
It would be nice if you could write a small review (here: forms.gle/eAjuWhCbiF7xbNWVA) of chapters you got for early access or for free, writing what you liked and didn't like and for early access, why you got it. It doesn't have to be detailed but it could help me to make better stories^^.