Is the estimate realistic. And what do the Omegafolks say about this one? It's a real grail, isn't it?
It certainly is a grail among grails. The gold versions were all the earlier c.910 (rather than the later c.911), ref. BA345.0801.
Rarity. Ash is correct that several reports spurred by requests from Bienne suggest that only 200 unnumbered solid gold flightmasters were produced, with only 20 having a solid gold bracelet and the other 180 on leather. See attached photo. However, other reports suggest that the gold flightmaster run may have actually been more limited, to as few as 30-50 examples total - with the Bienne-purported numbers representing something like an aspiration on the books which was never realized in production. Whatever the total run of examples, the first one was sold circa 1971 (purportedly sold to King Hussein of Jordan).
With respect to rarity, the follow-up to question to the "examples produced" mystery is the "examples surviving" mystery. With the gold rush of the 1980's, it is possible that several examples - especially the gold bracelet examples - were lost to the smelter. Then there's the normal attrition by history.
Distinctions. Note that these flightmasters are not only distinct in being made of solid gold, but they also exhibit other features unique only to the solid gold versions. Among those differences: raised gold hour markers, raised omega logo on the clasp, raised Omega logos. Of course, these dials also contain the designation makers "OM Swiss Made OM," designating the dial itself as being made "Or Massif" ("solid gold" in French).
Weight. One Japanese source purporting the gold bracelet versions to weigh in at 240-260 grams. This is confirmed by other sources as being in the 260 gram range. This is over twice the weight of a normal flightmaster. The flightline series of cases is simply dense, and these examples include a solid gold case back, and of course the bracelet is perhaps as heavy as the rest of the watch. The weight as being not only one of the two heaviest Omega's ever produced, but one of the heavier watches ever produced.