Not even for the highest end dealers unless there's a bidding war breaking out. If you sell a coin, expect to get about 75% of its value thanks to auction fees and such.
Actually, if you have a half million dollar COLLECTION, let alone single coin, you can expect any of the major coin auction houses to not only waive your seller's fee, but to actually pay you over the final hammer amount--somewhere usually in the 105 to 110 percent range. It's all negotiable.
I don't know if this is the right answer but if it was my coin I would probably consign it to Heritage or Stacks Bowers.
Who says the coin is worth $500,000? I tend to think coins of that rarity do not really have a 'book' value. With that said, I have seen major auctions where most of the coins go for around what was estimated prior to the auction, with some going for more. The Missouri cabinet of half cents was like this. Maybe more to the point, coins of this caliber sell better when they are being sold with other coins of the same caliber. If you have a $10 million collection, you are much more likely to get a good price on each coin then you are if the only coin you have is 1 $500,000 coin.
