If you choose the scented inks, the cost is an additional $3/bottle, bringing the pre-tax price to $13 for a 30ml bottle ($13/30ml = $.433/ml). Thus, for the scented inks, the price on Amazon ($.352 as mentioned) is
approximately 18% less expensive than the single-bottle price in this drop.
However, you are absolutely correct in that the same non-scented inks on Amazon tend to run considerably more - the few colors I had previously found available at the sub-$11 price seem to have been snatched up, and the general price makes these (again, *non*-scented) inks a great bargain by comparison, especially given the selection available versus the isolated examples similarly priced on Amazon. With one glaring caveat: no samples.
Which reminds me, thank you for the Goulet tip. I routinely rely on their swabs when I google a given color, but was unaware of the 5-ink comp feature. Nonetheless, do you realize there are nearly three-quarters of a MILLION different possible combinations by which you can choose five inks from a population of forty-one (749,398 to be exact)? Sorry, but I value my time way too much to spend a fair portion of the rest of it just to buy (more) J. Herbin ink, at least not when I'm equally happy with my Diamine inks and don't have to the dependency of having dedicate a significant chunk of time comparing colors (speaking of which, the Diamine drop running concurrently with this one is a better drop IMO). I think it is a reasonable expectation for the manufacturer - or anyone in the supply chain for that matter - to provide us with samples to help us make our selection, all things considered.