No serious advice.. there are at least 2-3 sellers on this forum, that handle natural abalone pearls. Perhaps not many of those are blister pearls, but since there aren't many and this might even be regarded as a more wearable shape then the irregular 'horn' ones... you should be able to get to some conclusion.
Although the large blisters should be rare, I remember of one more about the size of a dime and very tall. The owner had the same dillema: what on Earth is the pearl woth etc. I have tried to find that pearl's coordinates, but with no success -these are news from about 2.5 years ago!
