Do I have to pay for that alone?
Yes. Unless you wait until the municipality is ready.
I could now clean doorbells and ask in the street who wants to participate.
Good idea.
However, they would be pretty stupid if they did, right?
No. If there is someone who is in as much of a hurry as you are, then that person would be smart.
They could benefit from it anyway.
That depends ... If things go wrong, someone who doesn’t even want to build will incur unnecessary costs.
Can something like this be contractually regulated with the municipality so that I’m not left alone with the costs?
That depends ... on how the municipality envisions a change. The fact that there is already a legally binding development plan does not make things easier. Otherwise, the fourth section of the first part of the Building Code regulates cooperation with private individuals.
Is there anyone here who can give me advice on the best way to proceed?
Yes; wait and tirelessly court the key municipal council members and administrative staff.
I buy myself an electric car and everyone is allowed to use it.
No, rather: You have an electric car and want to install a wall box on the street where everyone can charge. Then only the neighbors who buy an electric car benefit; the others just miss another public parking space.
A house would fit in then.
Show me how you imagine that.