Or just passing along price increases in raw materials. A massive magical fire decimated barley and/or hop crops. PCs can investigate the source of the fire and find a stray fireball or something from nearby nefarious magical ritual, yadda yadda yadda.

Dwindling supply due to bbeg creating a portal to some other plane that allows demons to come through and they get out of his control and just decide to get hammered 24/7