> but wooden posts and barbed wire, it's less clear why those are so much more expensive now.

I am seeing way more active paddocks of grazing cattle now as compared to a couple of years ago. The world is complex and there is never an expiation that can be given in a short soundbite, but the primary driver is no doubt that higher beef prices compelled more people to try and raise cattle, which resulted in them needing supplies required to raise cattle, and fences are one of those things you need to establish a secure paddock. The increase in demand for fencing supplies, without a corresponding increase in supply, necessities an increase in price.