Nah, 20 doses chemical seems to be the clear RAW and RAI here. They deliberately added the 20x doses in this edition, while the toxin prices are EXACTLY the same in SR6 as in SR5. In other words, all as intended, the writers already knew how expensive toxins were, and the x20 was still added.
And it makes sense. You're exposing an entire area instead of using a single toxin vector (macing a single person, poisoning a drink, shooting a poisoned dart/arrow/dmso capsule round). At that point, the heavy toxins are expensive as hell yes. But teargas is just 150 nuyen per grenade.