Tell these so-called "alchemists" to go pluck themselves.
I can't recommend using garrison resources on this unless you have a bunch extra to blow. If you find yourself occasionally buying a Huge Ogre Cache on the AH, then it is probably not a good choice to do these missions.
YMMV, but on my server the garrison resources cost about 2 gold each buying caches on the AH. The last time I had one of these missions offered it was a pouch (2 rune average) for 30 resource. That comes out to about 30 gold per rune while the runes are on the AH for 5g each!
Garrison Timer Mobile App
Missions and Followers math for maximising success chance
Patch 6.1 Garrison Changes
Warlords of Draenor Garrison Missions Guide