That's a bit concreter than what I found, thanks. Yes, the prize drop is obviously crazy, which is why I thought about it in the first place
But it's tough to compare in wider sense of the word. First, it's basically an arbitrary restriction since alum was used for ages and not nearly so expensive. So it's only "pure" forms, but for other metals it's the less pure forms that are actually more interesting. Secondly, other metals weren't available at all, so couldn't have a prize to compare to, but if they had been available, speculatively they'd just been as expensive. So it's really got little to do with aluminum as such and all with "we can get tiny amounts but no more" - basically, it hit just the right window of exotic demand and very little supply.
But it's nonetheless an interesting piece of history. Obviously, tons of things got massively cheaper with time, but it's still a notable case I think.