I thought Jet A was substantially cheaper than 100LL but I recently looked at the prices throughout my area, and they are both priced at approximately $5.50 per gallon. I've never flown an aircraft that uses Jet A so I've never really paid attention, but I could have sworn that it was much cheaper than the leaded 100LL.
I can't find any articles or information online as to why Jet A is as expensive as 100LL. Avgas or 100LL is a specialty fuel and the only leaded fuel that is still made, so that explains why it is expensive, but Jet A is ubiquitous and produced in large quantity.
This previous question suggests the same thing that I'm saying, that Jet-A is cheaper because 100LL is a specialty fuel produced in small quantity, and Jet-A is widely available, etc. So, what has changed in the last 2 years? It can't just be supply and demand.