There's a great chance it was fake
It isn't really a "very rare" piece of history
I say 30 bucks.
Here is what the signed picture looks like:http://www.autogramme.com/shop/produktbilder/z_22535.jpg
Here is a photograph of Honecker's actual, confirmed signature:
It certainly looks like the same style of handwriting. If it is a forgery, it is a good one. The seller says it dates from 14 August 1989, two months before his resignation and 3 months before the demolition of the Berlin Wall began. It comes with a printed Certificate of Authenticity and "lifetime guarantee", whatever that's worth. They say it includes a document detailing when and where the signature was obtained.
The question is whether it is worth the price. The seller is asking US $168.30, and will sell it right away rather than through an auction. Pretty steep.
However, such items often go for considerably more. Yasser Arafat is going for US $468:http://www.autogramme.com/shop/produktbilder/18004.jpg
Other examples: David Ben Gurion's autograph is going for US $390.60 and Ronald Reagan's for US $899. You can get a document signed by Napoleon for US $2,970 and a personal note signed by Vladimir Lenin for US $110,000 (ouch; do they really expect someone to drop that much money on ebay?).