Welcome and Thank you for contributing to our interactive platform with your question :-)
I had a look and found different websites to check out.
First of all, Ebay Kleinanzeigen: https://www.ebay-kleinanzeigen.de/s-unterricht-kurse/berlin/guitar-lessons/k0c235l3331
If you scroll down, there is one person offering E-guitar lessons for 8€. There seem to be plenty of options. You can simply send them a message or call them!
Here is another option by a multilanguage cafe in Berlin for 10€ per hour (or less, if you are two or 3+ students): https://www.multilanguagecafe.com/course/berlin/guitar/710/
The only free option I found was the "Give Something Back to Berlin" Open Music School. They seem to offer a variety of music and singing classes for free: http://gsbtb.org/projects/open-music-school/
I hope these sources help and you find a cool teacher! Feel free to reach out to us again if you have any more questions.