This site tells you what everything costs.

http://www.weyounsworld.co.uk/downloads/other/ogame/index.html

We're a long way from having deathstars I'm affraid. A guy in my Uni1 Alliance has 3 of them! 200 Battleships can take one out tho.

Death Star = 5,000,000 Metal, 4,000,000 Crystal and 1,000,000 Deuterium. Plus to get Gravitron Tech to build one in the first place you need 3,000,000 in Energy. The only way to do that is to build about 8600 Solar Satelites. Not easy.