"An extract, once created, remains potent for 1 day before becoming inert, so an alchemist must re-prepare his extracts every day."
...and...
"If a spell normally has a costly material component, that component is consumed during the creation of that particular extract."
Don't make that stoneskin infusion until you're damn well ready to use it! Is this intentional? I can see how it might be; but if that's not a deliberate design decision, perhaps they should be allowed to keep a prepared infusion for more than a day, as a spellcaster can do with uncast spells.
This is actually a rather interesting point. Anything with a costly material component becomes a huge liability for the alchemist if he doesn't need it. It's not like a spell where the component doesn't go anywhere until used.
Allow the Alchemist to add the component as the final catalyst to activate it. (Pour the diamond dust in the prepared infusion, shake, drink.)
The Professor has Professed!
There is a specific part of the article:
"but it’s not uncommon for an alchemist to keep some (or even
all) of his daily extract slots open so that he can prepare
extracts in the field as needed."
Just don't prepare anything expensive. Prepare what you know you'll use over a couple of fights, your favorite buffs and some healing and leave a few extracts to be determined later in the day.