I'm in for at least 4. Now the real question is can you make the rubber boot? I'd be in for 4 of those as well!
The bung has been reverse engineered (I suspect he use a3D printer) so now there is a solid mold. The next step is to look into the correct rubber material.
At that point I will be able to get a rough idea of cost.
Stan:
to give you a point of reference for pricing, W+N sells them for 5.50euro each (Excl. VAT €4.62)
-- but then you may have to pay for the 32euro DHL shipping if that is all you are getting. hope this helps
Gavin
Is this the "blind plug", number 2 in this diagram:
http://www.realoem.com/bmw/showparts.do?model=3436&mospid=47811&btnr=41_1213&hg=41&fg=25