I'll contribute to this discussion by illustrating the quality of champlevé work coming out of China. Albeit, the quality is not near that described by caponerd. It can't be compared. However, for many airhead restorations, the investment in high quality work of the likes produced by caponerd and others in the art cannot be justified; thus there exists the market for reasonably priced repops like the one I recently purchased.
I found these 60mm champlevé repops on ebay, from the seller mhmetalheart. They looked from the Ebay description to be exactly what I was seeking. I wanted a reproduction roundel from an R27 or R51 with Serifed font and copper highlights (not chrome). This is what arrived today:
The base appears to be a brass rather than a copper. The enameling shows runs in a couple of places, a testament to their inferior pedigree. The enameling however is good enough for my purposes. It appears to be substantial and accurately applied on a plus side. The thickness of the base metal is approximately 2.5mm. These roundels are solid. The mounting holes are not beveled, meaning the mounting screws will be proud of the surface unless I countersink the holes myself (which I am planning). The backside of the roundel appears as below:
The price for these was very reasonable -- $30 per pair plus $16 shipping. I combined shipping on other parts I purchased which brought that price down. By comparison, purchasing original BMW roundels from the US would have cost me $40 per roundel plus shipping. The package took two weeks from Singapore to Ontario. I'm pleased with the roundels and could recommend them to others who are seeking reproductions but also are willing to make compromises in quality for price point.