Darren,
Can you get any photos?
If both the case and cross are original and the condition is good that price would be very fair.
Don't think I've ever seen an Assmann-marked piece and hopefully one of the other fellas who really studies these crosses will come to your aid.
Never rush into anything, do a bit of studying first. Try looking at some examples on
www.derrittmeister.com to get a bit more of a feeling for these units. Make sure you're 100%
comfortable with any deal that you might get into and ask about a return policy. Being happy is what this hobby is all about, nothing less.
Best of luck to you and please let us know how you make out, OK?
Bill