Hello,
can you give me more details about the user suggestion feature?
Do you want it to work 'facebook-style', that is when the user types something in a textarea field, they get suggestions of users to mention in their post? Or maybe you want this as a standalone feature, that is a simple text field that is dedicated for user search, which would load a list of users underneath that are matching the text input?
Shoot me a message here on Freelancer so that we can discuss this feature in detail. Once I know more details I'll be able to give you more accurate quote.
Best wishes,
Mateusz
EDIT: Okay, I have just translated 'Kontakt hinzufügen' and it looks like you're going to have a dedicated user search field with suggestions underneath. I have few more questions so please feel free to contact me via PM. Thanks!