Do prices change on a day to day basis?

I wanted to purchase a black dye, which I remember in Lions Arch a few weeks ago was around 2 plat. I checked today and it was 3843 gold.

What exactly is going on here?

Yes. Based on the amount sold etc etc etc.

people buy, price for it goes up, and price for other dyes go down by a tiny bit. people sell, price go down, and for other dye up a tiny bit.

that's why traders are not available in international districts, as to not mix up economies of the 3 different central servers

Supply and Demand .. basic econimcs.. and a major pain in the butt if you want black dye. All of the TRADER commodities.. be they dyes or materials fluctuate based on supply and the demand for them. .. Bunches of people want black dye and very very few people are selling it to teh traders.. That drives the prices through the roof. THe other things are a LOT more abundant in quantity and therefore are cheaper. In fact some of the crafting materials have gotten so common you are about better off selling them to the merchants rather than the traders.

Wow that is incredible to implement that into this game

It's an interesting way to help drain money out of the economy. They need more of that to help keep prices in check, although there will always be people selling stuff and undercutting the prices at the fixed vendors and thus keeping the money alive in the system.

I remember back when black dye was 770