If I can get a symmetry with a clip in ebonite you have at least one guaranteed sale from me if the price is under about $300. If you can already make that, PM me and I've got some money to give you.
I absolutely love the way you engraved that nib, the shadow effect on the art deco lettering is stunning. I actually even like the idea of how the nib will look tarnished. I love patina on silver and copper/bronze/brass
the pen itself(high gloss polished) costs around $150.
the clip, i am guessing $20-30.
as for the tarnishing effect, you will have total control over the tarnishing.
even if you mess up, you can start over again. thanks to the cleaning kit included.
you will need chemical called "liver of sulfer"
i never tried this either, but i am looking forward to trying the aged look!