I check some flute websites, the price of a few powell/yamaha models are reduced.
Is it because of christmas season? or bad economy?
I thought the price should keep going up.
Maybe it's a good time to buy now?

Most likely bad economy. The technical term is deflation. Prices rose faster than wages and now the makers are having to nearly sell stuff at cost to sell any at all.

Good time to buy, especially used, IF you have the money, that is...

it is probally the economic downturn as gordan brown keeps saying. the price of evrey thing is going down