score:2
It appears as if the current fine is 80 Euros if you admit the violation. There is no fine in the form of collecting points on your driver's license or the like, not even for those with German driver's licenses.
EDIT: After the edit of your question, it appears as if they are trying to find out who was the driver of the car (who is the person to be fined). You appear to be the owner of car and hence their point of contact. They officially ask for your input.
They write that they are allowed to fine you (the owner) in case you don't tell them (A lawyer may be able to tell you if that is actually true). They also inform you that you have them correct their information about you in case it is incorrect. They give you the opportunity to tell that you gave your car to somebody else who made the mistake of driving into a zone of environmental protection. If you give them information, they will decide based on the information to forget about the issue or to proceed (which most likely means issuing a fine).
They also write that in case you don't answer, it would be inappropriate for them to continue finding out who had the car. In this case, they will charge you for the (administrative) cost incurred so far. This appears to contradict what they write earlier and a lawyer may be able to tell if that is actually true. I find the sentence "Zu dieser Kostenentscheidung hΓΆre ich Sie hiermit an." in that context quite surprising and it may encode something legalese.