77,35 EUR [inkl. 19% MwSt zzgl. Versandkosten] + 3 Euro transport.
Before buying I got some very useful advice from the Australian guru Paul Burkes and a quote from a nice guy called Bob Dolby from Acril Convex Pty Ltd
Acril Convex have the perfect solution, which is correct mirror ; a 600 x300 quarter sphere (Half Dome mirror). In Acril's catalogue, the mirror has the reference 20534. My only concern is that the company needs to ship the first surface mirror from Australia and therefore, the price increases on top of the first surface mirror price, which is already five or six times the price of the polymer mirror I just got. In the long run, I think this is the way forward but if it so expensive and subject to scratches, I may investigate other techniques for dome projection as explained somewhere in this diary.