Is there some sort of global economy in place?

So to work on my smithing and enchanting skills, I have been creating a TON of banish daggers lately. I've noticed that after I had sold enough, the prices had started to go down a bit. Just now, however, I was able to sell one for practically the same price I was at the beginning. Is there some sort of economy that I flooded with banish daggers for a while, or is it more likely I just didn't realize I had a certain piece of gear or something on?