Then you make many enchanted items like iron daggers with turn undead they are worth around 700 gold, however as you make many the price can drop down to 400.
Items with banish start out at 1200 but also drop in value.

Now here is the strange thing, if you don't make more and just store them the price jump up to default again after some time.

This makes it smart to store them over selling unless you need the money now, if you just do it to buy a house it might be smart to wait, however I don't know how long you have to wait.

Anybody know more about this strange effect.

I have not noticed this in my game but Ill keep a look out for it.
If it is indeed as you say then 'affecting the economy' might be in the game after all in one form or another, though it really doesnt do much or I would have noticed earlier.
What probably happens is supply and demand. If there is a high supply, the price drops.

it is just like oblivion's system, the more of an object an NPC has the less they will buy/sell it for