Re: €100 (~$112) or €200 (~$225)
Exactly my reaction. I would simply turn down a contact that small for exactly those reasons, even if it did not involve real effort (which this does if you do it properly).
If approached to do this I would reply that they do not need to do this, but what they do need to do is pick a library or framework that provides this and I would help them do that for a fee.
If some naive enough not to know that already is "developing a social networking site" they probably think:
1. They can build a Facebook clone for a thousand quid.
2. Thinks people will actually abandon Facebook or Twitter to use their site
So it will attract developers who do not mind getting involved in a project that is certain to fail.